0001397702-22-000012 | 10-K | XBRL Viewer

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Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net loss	$ (49,811)	$ (47,365)	$ (52,415)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	1,032	789	712
Stock-based compensation expense	14,612	7,226	2,977
Change in fair value of redeemable convertible preferred stock warrant liability			21,030
Amortization of premiums (accretion of discounts) on investments, net	577	304	(309)
Amortization of debt discount and debt issuance costs	158	66	46
Amortization of right-of-use asset	887	602	582
Non-cash interest expense		241	672
Loss on extinguishment of debt		1,119
Loss on disposal of property and equipment	9	52
Change in provision for doubtful accounts receivable	6	(32)	23
Provision for excess and obsolete inventories	77	117	118
Changes in operating assets and liabilities:
Accounts receivable	(2,769)	(437)	(2,241)
Inventories	(5,563)	(2,161)	(4,696)
Prepaid expenses and other current assets	(772)	250	(1,471)
Other assets	(117)	210	552
Accounts payable	(1,159)	592	615
Accrued liabilities	4,418	146	4,964
Other liabilities	(520)	26	(769)
Repayment of interest paid in kind		(3,813)
Net cash used in operating activities	(38,935)	(42,068)	(29,610)
Cash flows from investing activities
Purchases of property and equipment	(4,758)	(842)	(535)
Proceeds from sale of property and equipment	2
Purchases of investments		(79,906)	(69,421)
Proceeds from maturity of investments	77,400	71,355
Net cash provided by (used in) investing activities	72,644	(9,393)	(69,956)
Cash flows from financing activities
Proceeds from public offerings, net of underwriting discount, commissions and offering costs paid		70,568	109,352
Proceeds from long-term debt, net		48,506
Proceeds from issuance of common stock	6,946	5,168	2,590
Principal repayment of long-term debt		(40,000)
Payments of prepayment penalty and lender fees		(2,496)
Proceeds from disgorgement of short-swing profits, net	32
Net cash provided by financing activities	6,978	81,746	113,757
Net change in cash, cash equivalents and restricted cash	40,687	30,285	14,191
Cash, cash equivalents and restricted cash, beginning of period	69,776	39,491	25,300
Cash, cash equivalents and restricted cash, end of period	110,463	69,776	39,491
Supplemental disclosure of cash flow information
Cash paid for interest	2,360	7,917	4,234
Noncash investing and financing activities:
Accounts payable and accrued liabilities for purchases of property and equipment	1,138	108	32
Unpaid deferred offering costs		$ 25
Right-of-use asset obtained in exchange for lease obligation	$ 3,307		3,982
Net exercise of redeemable convertible preferred stock warrants to preferred stock			37,121
Conversion of redeemable convertible preferred stock to common stock upon initial public offering			144,140
Redeemable convertible preferred stock warrants outstanding
Cash flows from financing activities
Proceeds from exercise of warrants			1,784
Common stock warrants outstanding
Cash flows from financing activities
Proceeds from exercise of warrants			$ 31

Stock Option Plans (RSUs) (Details) - Restricted Stock Units [Member] - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Number of Restricted Stock Units
Beginning balance (in shares)	68,396
Restricted stock granted (in shares)	524,023	69,040
Restricted stock vested (in shares)	(34,964)
Restricted stock forfeited (in shares)	(27,181)	(644)
Ending balance (in shares)	530,274	68,396
Expected to vest (in shares)	530,274
Weighted Average Grant Date Fair Value
Beginning balance (in USD per share)	$ 46.16
Restricted stock granted (in USD per share)	53.64	46.14
Restricted stock vested (in USD per share)	49.95
Restricted stock forfeited (in USD per share)	51.99	44.62
Ending balance (in USD per share)	53.01	$ 46.16
Expected to vest (in USD per share)	$ 53.01

Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	May 31, 2020	Apr. 30, 2019	Dec. 31, 2020	Dec. 31, 2019
Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) [Abstract]
Offering costs	$ 707	$ 2,481	$ 4,457	$ 10,961

Balance Sheet Components (Tables)	12 Months Ended
Balance Sheet Components (Tables)	Dec. 31, 2021
Balance Sheet Components [Abstract]
Fair Value of the Available-For-Sale Investments	December 31, 2020 Gross Unrealized Estimated Amortized Cost Gains Losses Fair ValueMoney market funds$ 60,295 $— $— $ 60,295Commercial paper 39,577 — — 39,577Corporate bonds/notes 7,970 — (1) 7,969U.S. government securities 38,430 42 (2) 38,470 $ 146,272 $ 42 $ (3) $ 146,311 Classified as: Cash equivalents $ 68,295Short-term investments 78,016 $ 146,311
Fair Value of Cash Equivalents, Short-Term and Long-Term Equivalents	December 31,‎2021 December 31,‎2020Amounts maturing within one year $ 21,062 $ 146,311Amounts maturing after one year through two years — — $ 21,062 $ 146,311
Available-For-Sale Investments in Unrealized Loss Position	December 31, 2020 Less than 12 monthsAssets: Fair Value Unrealized LossCorporate bonds/notes $ 5,369 $ (1)U.S. government securities 10,128 (2) $ 15,497 $ (3)
Schedule of Inventories	December 31, 2021 2020Raw materials $ 2,447 $ 1,785Finished products 15,437 10,599 17,884 12,384Less: Reserve for excess and obsolete (33) (2,395) $ 17,851 $ 9,989
Property, Plant and Equipment	December 31, 2021 2020Furniture and fixtures$ 1,005 $ 726Equipment 2,945 1,699Software 284 226Leasehold improvements 2,050 2,043 6,284 4,694Less: Accumulated depreciation (3,330) (2,332)Add: Construction-in-progress 4,743 482 $ 7,697 $ 2,844
Schedule of Accrued Liabilities	December 31, 2021 2020Accrued payroll and related expenses $ 13,898 $ 9,573Provision for sales returns 359 820Accrued professional services 2,039 2,520Recall replacement obligation 11 1,696Operating lease liability 1,294 850Accrued royalty expense 687 518Deferred revenue 157 206Accrued travel expenses 590 237Accrued clinical expenses 99 113Accrued other expenses 668 424 $ 19,802 $ 16,957

Balance Sheet Components - (Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 6,284	$ 4,694
Less: Accumulated depreciation and amortization	(3,330)	(2,332)
Property and equipment, net	7,697	2,844
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,005	726
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,945	1,699
Software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	284	226
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,050	2,043
Construction-in-progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,743	$ 482

Stock Option Plans (Stock-based Compensation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 14,612	$ 7,226	$ 2,977
Cost of Goods Sold [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	635	339	179
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,909	1,110	426
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 11,068	$ 5,777	$ 2,372

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
Stockholders' Equity (Deficit) (Tables)	Dec. 31, 2021
Stockholders' Equity (Deficit) [Abstract]
Schedule Of Common Stokc Reserved For Future Issuances [Table Text Block]	December 31, 2021 2020Exercise of options under stock plan 3,780,939 4,237,828Issuance of options and restricted stock units under stock plan 2,477,212 1,790,687Issuance of common stock under employee stock purchase plan 922,097 632,377 7,180,248 6,660,892

Summary of Significant Accounting Policies - Income Taxes (Narrative) (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies [Abstract]
Provision for income taxes
Liability for uncertain tax positions	$ 0

Stock Option Plans (Information by Exercise Price) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding (in shares)	3,780,939	4,237,828	4,310,790	4,364,377
Weighted Average Remaining Contractual Term (in Years)	6 years 8 months 15 days	7 years 4 months 17 days	7 years 3 months 7 days	7 years 4 months 9 days
Weighted Average Exercise Price (in USD per share)	$ 20.45	$ 16.56	$ 7.91	$ 3.79
Number Exercisable (in shares)	2,732,674
Weighted Average Exercise Price (in USD per share)	$ 13.64
Exercise Price One
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit	1.35
Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit	$ 3.16
Options Outstanding (in shares)	868,256
Weighted Average Remaining Contractual Term (in Years)	4 years 6 months 29 days
Weighted Average Exercise Price (in USD per share)	$ 2.05
Number Exercisable (in shares)	868,256
Weighted Average Exercise Price (in USD per share)	$ 2.05
Exercise Price Two [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit	4.73
Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit	$ 7.10
Options Outstanding (in shares)	577,759
Weighted Average Remaining Contractual Term (in Years)	6 years 2 months 1 day
Weighted Average Exercise Price (in USD per share)	$ 5.74
Number Exercisable (in shares)	542,305
Weighted Average Exercise Price (in USD per share)	$ 5.71
Exercise Price Three [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit	8.27
Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit	$ 12.41
Options Outstanding (in shares)	490,391
Weighted Average Remaining Contractual Term (in Years)	6 years 21 days
Weighted Average Exercise Price (in USD per share)	$ 11.74
Number Exercisable (in shares)	470,037
Weighted Average Exercise Price (in USD per share)	$ 11.83
Exercise Price Four [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit	20.00
Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit	$ 30.00
Options Outstanding (in shares)	616,871
Weighted Average Remaining Contractual Term (in Years)	7 years 3 months 3 days
Weighted Average Exercise Price (in USD per share)	$ 20.00
Number Exercisable (in shares)	400,815
Weighted Average Exercise Price (in USD per share)	$ 20.00
Exercise Price Five
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit	30.93
Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit	$ 46.40
Options Outstanding (in shares)	682,913
Weighted Average Remaining Contractual Term (in Years)	8 years 1 month 13 days
Weighted Average Exercise Price (in USD per share)	$ 33.60
Number Exercisable (in shares)	308,065
Weighted Average Exercise Price (in USD per share)	$ 34.34
Exercise Price Six
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit	47.20
Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit	$ 70.80
Options Outstanding (in shares)	544,749
Weighted Average Remaining Contractual Term (in Years)	8 years 10 months 9 days
Weighted Average Exercise Price (in USD per share)	$ 57.22
Number Exercisable (in shares)	143,196
Weighted Average Exercise Price (in USD per share)	$ 57.48

Subsequent Events (Details) - shares	1 Months Ended		12 Months Ended
Subsequent Events (Details) - shares	Feb. 28, 2022	Jan. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
2019 Equity Incentive Plan [Member] \| Subsequent Event
Subsequent Event [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized		1,399,235
ESPP, 2019 [Member] \| Subsequent Event
Subsequent Event [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized		349,808
Restricted Stock Units [Member]
Subsequent Event [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period			524,023	69,040
Restricted Stock Units [Member] \| 2019 Equity Incentive Plan [Member] \| Subsequent Event
Subsequent Event [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	21,357	21,357

Summary of Significant Accounting Policies (Tables)	12 Months Ended
Summary of Significant Accounting Policies (Tables)	Dec. 31, 2021
Summary of Significant Accounting Policies [Abstract]
Schedule of Cash and Cash Equivalents	December 31, 2021 2020Cash and cash equivalents $ 110,231 $ 69,466Restricted cash 232 310Total cash, cash equivalents and restricted cash $ 110,463 $ 69,776
Net Loss Per Share Determination	Year Ended December 31, 2021 2020 2019Net loss $ (49,811) $ (47,365) $ (52,415)Weighted average common stock outstanding used to compute net loss per share, basic and diluted 34,635,358 32,965,539 22,956,679Net loss per share, basic and diluted $ (1.44) $ (1.44) $ (2.28)
Schedule of Potentially Dilutive Securities Outstanding Excluded from Diluted Weighted Average Shares Outstanding	December 31, 2021 2020 2019Common stock options 3,780,939 4,237,828 4,310,790Restricted stock units 530,274 68,396 —Total 4,311,213 4,306,224 4,310,790

Summary of Significant Accounting Policies - Revenue Recognition (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies [Abstract]
Unbilled receivables	$ 87	$ 71

Summary of Significant Accounting Policies - Property and Equipment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Asset Impairment Charges	$ 0	$ 0	$ 0
Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years

Recent Accounting Pronouncements	12 Months Ended
Recent Accounting Pronouncements	Dec. 31, 2021
Recent Accounting Pronouncements [Abstract]
Recent Accounting Pronouncements	3. Recent Accounting Pronouncements Recently Adopted Accounting Standards Effective January 1, 2021, the Company adopted ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires measurement and recognition of expected credit losses for most financial assets and certain other instruments. In addition, Topic 326 also provides new guidance related to the measurement of expected credit losses on the Company’s allowance for bad debt for accounts receivable, which is estimated upon assessment of various factors including historical collection experience, current and future economic market conditions and a review of the current aging status and financial condition of the Company’s customers. The Company adopted the new standard using a modified retrospective transition method, which required a cumulative-effect adjustment, if any, to the opening balance of accumulated deficit to be recognized on the date of adoption. The Company did not have any cumulative-effect adjustments as of the date of adoption. Effective January 1, 2021, the Company adopted ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which enhances and simplifies various aspects of the income tax accounting guidance related to intra-period tax allocation, interim period accounting for enacted changes in tax law, and the year-to-date loss limitation in interim period tax accounting. ASU 2019-12 also amends other aspects of the guidance to reduce complexity in certain areas. The adoption did not have a material impact on the Company's financial statements and related disclosures. Recently Issued Accounting Standards In October 2021, the FASB issued ASU No. 2021-08, Business Combinations (Topic 805): Accounting for Contract Assets and Contract Liabilities from Contracts with Customers (“ASU 2021-08”), which creates an exception to the general recognition and measurement principle in ASC 805 by requiring companies to apply ASC 606 to recognize and measure contract assets and contract liabilities from contracts with customers acquired in a business combination. The guidance additionally clarifies that companies should apply the definition of a performance obligation in ASC 606 when recognizing contract liabilities assumed in a business combination. The Company will early adopt ASU 2021-08 as of January 1, 2022 on a prospective basis. The impact of the adoption of ASU 2021-08 cannot currently be determined, as it is dependent on future business combinations that the Company may enter into.

- Definition

The entire disclosure for change in accounting principle. Includes, but is not limited to, nature, reason, and method of adopting amendment to accounting standards or other change in accounting principle.

+ References

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-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 65
-Paragraph 2
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641

Reference 30: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 10
-Section 65
-Paragraph 4
-Subparagraph (e)(2)
-URI http://asc.fasb.org/extlink&oid=122640432&loc=SL121648383-210437

Reference 31: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=124431687&loc=d3e22499-107794

Reference 32: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 848
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=122150657&loc=SL122150809-237846

Reference 33: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 65
-Paragraph 8
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=123459177&loc=SL121830611-158277

Reference 34: http://www.xbrl.org/2003/role/disclosureRef
-Topic 848
-SubTopic 10
-Name Accounting Standards Codification
-Section 65
-Paragraph 2
-Publisher FASB
-Subparagraph (c)

+ Details

Balance Sheet Components - Fair Value of Cash Equivalents, Short-Term and Long-Term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Components [Abstract]
Amounts maturing within one year	$ 21,062	$ 146,311
Total	$ 21,062	$ 146,311

Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Redeemable Convertible Preferred Stock Convertible Preferred Stock	Redeemable Convertible Preferred Stock Series C Preferred Stock [Member]	Redeemable Convertible Preferred Stock	Common Stock Convertible Preferred Stock	Common Stock Common Class A [Member]	Common Stock	Additional Paid-in Capital Convertible Preferred Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	Convertible Preferred Stock	Total
Beginning balance (in shares) at Dec. 31, 2018			21,233,190			1,135,310
Beginning balance at Dec. 31, 2018			$ 105,235			$ 1		$ 4,557	$ (139,111)			$ (134,553)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of Series C preferred stock warrants			$ 1,784
Exercise of Series C preferred stock warrants (in shares)			292,361
Exercise of common stock warrants								31				31
Exercise of common stock warrants (in shares)						3,764
Issuance of common stock						$ 6		109,113				109,119
Issuance of common stock (in shares)						6,000,000
Conversion of preferred stock upon IPO	$ (144,140)	$ 37,121		$ 23			$ 144,117				$ 144,140
Conversion of preferred stock upon IPO (in shares)	(23,178,555)	1,653,004		23,178,555	2,204
Exercise of stock options						$ 1		1,541				$ 1,542
Exercise of stock options (in shares)						873,786						873,786
Issuance of common stock under employee stock purchase plan								1,048				$ 1,048
Issuance of common stock under employee stock purchase plan (in shares)						61,648
Stock-based compensation								2,977				2,977
Net loss									(52,415)			(52,415)
Change in unrealized gains on investments, net										$ 2		2
Ending balance (in shares) at Dec. 31, 2019						31,255,267
Ending balance at Dec. 31, 2019						$ 31		263,384	(191,526)	2		71,891
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock						$ 2		70,541				70,543
Issuance of common stock (in shares)						1,923,076
Exercise of stock options						$ 1		3,486				$ 3,487
Exercise of stock options (in shares)						1,018,779						1,018,779
Issuance of common stock under employee stock purchase plan								1,681				$ 1,681
Issuance of common stock under employee stock purchase plan (in shares)						52,527
Stock-based compensation								7,226				7,226
Net loss									(47,365)			(47,365)
Change in unrealized gains on investments, net										37		37
Ending balance (in shares) at Dec. 31, 2020						34,249,649
Ending balance at Dec. 31, 2020						$ 34		346,318	(238,891)	39		107,500
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options						$ 1		4,841				$ 4,842
Exercise of stock options (in shares)						643,507						643,507
Issuance of common stock upon release of restricted stock units (in shares)						34,964
Issuance of common stock under employee stock purchase plan								2,104				$ 2,104
Issuance of common stock under employee stock purchase plan (in shares)						52,776
Stock-based compensation								14,612				14,612
Disgorgement of short-swing profits, net								32				32
Net loss									(49,811)			(49,811)
Change in unrealized gains on investments, net										$ (39)		(39)
Ending balance (in shares) at Dec. 31, 2021						34,980,896
Ending balance at Dec. 31, 2021						$ 35		$ 367,907	$ (288,702)			$ 79,240

Summary of Significant Accounting Policies - Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Voluntary Recall
Valuation Allowance [Line Items]
Other Assets, Current		$ 4,160
Direct Costs [Member]
Valuation Allowance [Line Items]
Other Assets, Current	$ 335

Commitments and Contingencies - Lease (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset	$ 5,219	$ 2,798
Operating Lease, Liability	7,041	3,700
Operating lease costs	1,234	870	$ 870
Operating lease liabilities	$ 34	$ 769	$ 721
Weighted average discount rate	6.50%	6.50%
Weighted average remaining lease term	5 years 10 months 9 days	3 years 9 months 29 days
Headquarters [Member]
Lessee, Lease, Description [Line Items]
Renewal term	5 years
Additional Office, Laboratory And Manufacturing Space [Member]
Lessee, Lease, Description [Line Items]
Renewal term	5 years
Operating Lease, Right-of-Use Asset	$ 3,307
Operating Lease, Liability	$ 3,307

Debt (Tables)	12 Months Ended
Debt (Tables)	Dec. 31, 2021
Debt [Abstract]
Future Maturities Under the Term Loan Agreement	Year Ending December 31: Amount2022 $ 6,2572023 25,7492024 21,457 53,463Less: Amount representing interest (4,463)Less: Amount representing debt discount and debt issuance costs (309)Present value of minimum payments $ 48,691

Recent Accounting Pronouncements (Policies)	12 Months Ended
Recent Accounting Pronouncements (Policies)	Dec. 31, 2021
Recent Accounting Pronouncements [Abstract]
Recent Accounting Pronouncements	Recently Adopted Accounting Standards Effective January 1, 2021, the Company adopted ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires measurement and recognition of expected credit losses for most financial assets and certain other instruments. In addition, Topic 326 also provides new guidance related to the measurement of expected credit losses on the Company’s allowance for bad debt for accounts receivable, which is estimated upon assessment of various factors including historical collection experience, current and future economic market conditions and a review of the current aging status and financial condition of the Company’s customers. The Company adopted the new standard using a modified retrospective transition method, which required a cumulative-effect adjustment, if any, to the opening balance of accumulated deficit to be recognized on the date of adoption. The Company did not have any cumulative-effect adjustments as of the date of adoption. Effective January 1, 2021, the Company adopted ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which enhances and simplifies various aspects of the income tax accounting guidance related to intra-period tax allocation, interim period accounting for enacted changes in tax law, and the year-to-date loss limitation in interim period tax accounting. ASU 2019-12 also amends other aspects of the guidance to reduce complexity in certain areas. The adoption did not have a material impact on the Company's financial statements and related disclosures. Recently Issued Accounting Standards In October 2021, the FASB issued ASU No. 2021-08, Business Combinations (Topic 805): Accounting for Contract Assets and Contract Liabilities from Contracts with Customers (“ASU 2021-08”), which creates an exception to the general recognition and measurement principle in ASC 805 by requiring companies to apply ASC 606 to recognize and measure contract assets and contract liabilities from contracts with customers acquired in a business combination. The guidance additionally clarifies that companies should apply the definition of a performance obligation in ASC 606 when recognizing contract liabilities assumed in a business combination. The Company will early adopt ASU 2021-08 as of January 1, 2022 on a prospective basis. The impact of the adoption of ASU 2021-08 cannot currently be determined, as it is dependent on future business combinations that the Company may enter into.

Fair Value Measurements (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	$ 0	$ 0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	0	0
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	21,062,000	146,311,000
Recurring [Member] \| Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	21,062,000	60,295,000
Recurring [Member] \| Commercial Papers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		39,577,000
Recurring [Member] \| Corporate Bonds/Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		7,969,000
Recurring [Member] \| U.S. Government Securitie [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		38,470,000
Recurring [Member] \| Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	21,062,000	60,295,000
Recurring [Member] \| Level 1 [Member] \| Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 21,062,000	60,295,000
Recurring [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		86,016,000
Recurring [Member] \| Level 2 [Member] \| Commercial Papers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		39,577,000
Recurring [Member] \| Level 2 [Member] \| Corporate Bonds/Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		7,969,000
Recurring [Member] \| Level 2 [Member] \| U.S. Government Securitie [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		$ 38,470,000

Summary of Significant Accounting Policies - Redeemable Convertible Preferred Stock (Narrative) (Details) - Common Stock $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) shares
Class of Stock [Line Items]
Conversion of preferred stock upon IPO (in shares) \| shares	23,178,555
Conversion of preferred stock upon IPO \| $	$ 144,140

401(k) Plan	12 Months Ended
401(k) Plan	Dec. 31, 2021
401(k) Plan [Abstract]
401(k) Plan	12. 401(k) Plan The Company has a qualified retirement plan under section 401(k) of the Internal Revenue Code (“IRC”) under which participants may contribute up to 90% of their eligible compensation, subject to maximum deferral limits specified by the IRC. The Company may make a discretionary matching contribution to the 401(k) plan and may make a discretionary employer contribution to each eligible employee each year. Through December 31, 2019, the Company has made no contributions to the 401(k) plan. Beginning in January 2020, the Company started matching employees' contributions to the 401(k) plan at 50% of the first 5% of compensation deferred to the 401(k) plan. The Company's matching contributions were $1,313,000 and $959,000 for the years ended December 31, 2021 and 2020, respectively.

Redeemable Convertible Preferred Stock - Narrative (Details) - $ / shares	24 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	May 31, 2020	Aug. 31, 2019	Apr. 30, 2019
Temporary Equity [Line Items]
Stock issued, price per share (in USD per share)			$ 39.00	$ 39.50	$ 20.00
Convertible Preferred Stock
Temporary Equity [Line Items]
Stock issued, price per share (in USD per share)	$ 20.00
Shares of common stock converted (in shares)	1,945,365
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2021
Summary of Significant Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Preparation The accompanying financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (“U.S. GAAP”). Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts and disclosures reported in the financial statements. Management uses judgment when making estimates related to provisions for accounts receivable and excess and obsolete inventories, the valuation of deferred tax assets, the reserves for sales returns, stock-based compensation, and for periods prior to the Company's IPO, the valuation of common stock and redeemable convertible preferred stock warrants. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately differ from these estimates and assumptions. Due to the coronavirus (“COVID-19”) pandemic, there has been continued uncertainty and disruption in the global economy, supply chain, financial markets and increased labor shortages. While some of the uncertainties began to lift throughout the first half of 2021, new virus variants, and increased infection rates during the second half of 2021 continue to make the current COVID-related environment highly volatile and uncertain. These challenges continued to impact the number of TCAR procedures in 2021, with procedure volumes impacted by increased COVID-19 hospitalizations and hospital capacity constraints due to the COVID-19 and its variants. The Company is not aware of any specific event or circumstance that would require an update to its estimates or judgments or a revision of the carrying value of its assets or liabilities as of December 31, 2021. The Company has also considered information available to it as of the date of issuance of these financial statements and is not aware of any specific events or circumstances that would require an update to its estimates or judgments, or a revision to the carrying value of its assets or liabilities. These estimates may change as new events occur and additional information becomes available. Actual results could differ materially from these estimates. Fair Value of Financial Instruments The Company has evaluated the estimated fair value of its financial instruments as of December 31, 2021 and 2020. The carrying amounts of certain of the Company’s financial instruments, which include cash equivalents, short-term investments, restricted cash, accounts receivable, accounts payable and accrued liabilities approximate their respective fair values because of the short-term nature of these instruments. Management believes that its short-term and long-term debt bears interest at the prevailing market rates for instruments with similar characteristics (Level 2 within the fair value hierarchy); accordingly, the carrying value of this instrument approximates its fair value. Prior to the Company's IPO, fair value accounting was applied to the redeemable convertible preferred stock warrant liability. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with an original maturity of three months or less at the time of purchase to be cash equivalents. Cash equivalents are considered available-for-sale marketable securities and are recorded at fair value, based on quoted market prices. As of December 31, 2021, the Company’s cash equivalents are comprised of investments in money market funds. As of December 31, 2020, the Company’s cash equivalents comprised investments in money market funds and commercial paper. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the balance sheets that sum to the total of the same amounts shown in the statements of cash flows (in thousands): December 31, 2021 2020Cash and cash equivalents $ 110,231 $ 69,466Restricted cash 232 310Total cash, cash equivalents and restricted cash $ 110,463 $ 69,776 Restricted cash as of December 31, 2021 and 2020 consists of a letter of credit of $232,000 and $310,000, respectively, representing collateral for the Company’s facility lease in California. Investments Short-term investments consist of debt securities classified as available-for-sale and have original maturities greater than 90 days, but less than one year as of the balance sheet date. Long-term investments have maturities greater than one year as of the balance sheet date. All investments are recorded at fair value based on the fair value hierarchy. Money market funds are classified within Level 1 of the fair value hierarchy, and commercial paper, corporate bonds/notes, United States Government securities, and asset-backed securities are classified within Level 2 of the fair value hierarchy. Unrealized gains and losses, deemed temporary in nature, are reported as a separate component of accumulated other comprehensive income (loss). The cost of available-for-sale investments sold is based on the specific-identification method. Realized gains and losses are included in earnings and are derived for specific-identification method for determining the costs of investments sold and were insignificant for the year ended December 31, 2021, 2020 and 2019. Amortization of premiums and accretion of discounts are reported as a component of interest income. A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the investment. The Company evaluates the securities in an unrealized loss position for expected credit losses by considering factors such as historical experience, market data, issuer-specific factors, current economic conditions and credit ratings. Concentration of Credit Risk, and Other Risks and Uncertainties The Company is subject to risks related to public health crises such as the global pandemic associated with COVID-19. The COVID-19 outbreak has negatively impacted, and may continue to negatively impact the Company’s operations, its revenue and overall financial condition by significantly decreasing the number of TCAR procedures performed. The number of TCAR procedures performed, similar to other surgical procedures, has significantly decreased as health care organizations globally prioritized the treatment of patients with COVID-19. In the past governmental authorities have recommended, and in certain cases required, that elective, specialty and other procedures and appointments, be suspended or canceled to focus limited resources and personnel and hospital capacity toward the treatment of COVID-19 and to avoid exposing patients to COVID-19. These measures and challenges will likely continue for the duration of the pandemic, which is uncertain, and will continue to negatively impact the Company’s revenue while the pandemic continues. New virus variants, and increased infection rates continue to make the current COVID-related environment highly volatile and uncertain. Financial instruments that potentially subject the Company to credit risk consist of cash and cash equivalents, investments and accounts receivable to the extent of the amounts recorded on the balance sheet. Cash, cash equivalents, and investments are deposited in financial institutions which, at times, may be in excess of federally insured limits. Cash equivalents are invested in highly rated money market funds. The Company invests in a variety of financial instruments, such as, but not limited to, commercial paper, corporate bonds/notes, United States Government securities, asset-backed securities and, by policy, limits the amount of credit exposure with any one financial institution or commercial issuer. The Company has not experienced any material losses on its deposits of cash and cash equivalents or investments during the years ended December 31, 2021 and 2020. The Company’s accounts receivable are due from a variety of health care organizations in the United States. At December 31, 2021 and 2020, no customer represented 10% or more of the Company’s accounts receivable. For the years ended December 31, 2021, 2020 and 2019, there were no customers that represented 10% or more of revenue. The Company provides for uncollectible amounts when specific credit problems are identified. In doing so, the Company analyzes historical bad debt trends, customer credit worthiness, current economic trends and changes in customer payment patterns when evaluating the adequacy of the allowance for expected credit losses on customer accounts. The Company manufactures certain of its commercial products in-house. Certain of the Company’s product components and sub-assemblies continue to be manufactured by sole suppliers, the most significant of which is the ENROUTE Transcarotid Stent System, manufactured by Cordis Corporation. Disruption in component or sub-assembly supply from these manufacturers or from in-house production would have a negative impact on the Company’s financial position and results of operations. The Company is subject to certain risks, including that its devices may not be approved or cleared for marketing by governmental authorities or be successfully marketed. There can be no assurance that the Company’s products will achieve widespread adoption in the marketplace, nor can there be any assurance that existing devices or any future devices can be developed or manufactured at an acceptable cost and with appropriate performance characteristics. The Company is also subject to risks common to companies in the medical device industry, including, but not limited to, new technological innovations, dependence upon government and third-party payers to provide adequate coverage and reimbursement, dependence on key personnel and suppliers, protection of proprietary technology, product liability claims, and compliance with government regulations. Existing or future devices developed by the Company may require approvals or clearances from the FDA or international regulatory agencies. In addition, in order to continue the Company’s operations, compliance with various federal and state laws is required. If the Company were denied or delayed in receiving such approvals or clearances, it may be necessary to adjust operations to align with the Company’s currently approved portfolio. If clearance for the products in the current portfolio were withdrawn by the FDA, this would have a material adverse impact on the Company. Voluntary Recall In January and February 2021, the Company announced the voluntary recall of certain lots of its ENROUTE Transcarotid Stent System, manufactured by one of its third-party suppliers, Cordis. The decision to recall these lots was based on complaints received about tips detaching from the stent delivery system as well as internal testing that the Company conducted. The Company believes the root cause of the detachment was a single operator at Cordis, who, over a specific timeframe, produced lots in which a small number of units were not reliably manufactured to specification. As a result of the voluntary recall the Company reflected a current asset of $4,160,000 on its balance sheet as of December 31, 2020, relating to the replacement lots and other direct costs to be received from Cordis. This amount included $2,227,000 of recalled ENROUTE stent delivery systems held in the Company's inventory as of December 31, 2020, $1,696,000 of ENROUTE stent delivery systems in the process of being returned from its customers and other direct costs of $237,000. In addition, the Company established an accrual of $1,696,000 relating to its obligation to provide replacement ENROUTE stent delivery systems to its customers as of December 31, 2020. As of December 31, 2021, the Company has a current asset of $335,000 on its balance sheet relating to other direct costs that remain to be reimbursed from Cordis. In addition, as of December 31, 2021, the Company has a remaining accrual of $11,000 relating to its obligation to provide replacement ENROUTE stent delivery systems to its customers. Accounts Receivable Trade accounts receivable are recorded at the invoiced amount and do not bear interest. The Company estimates allowances for expected credit losses. Specifically, the Company makes estimates on the collectability of customer accounts based primarily on analysis of historical trends and experience and changes in customers’ financial condition. The Company uses its judgment, based on the best available facts and circumstances, and records an allowance against amounts due to reduce the receivable to the amount that is expected to be collected. These specific allowances are reevaluated and adjusted as additional information is received that impacts the amount reserved. During the years ended December 31, 2021, 2020 and 2019, the Company did not experience any material credit-related losses. Inventories Inventories are valued at the lower of cost to purchase or manufacture the inventory or net realizable value. Cost is determined using the first-in, first-out method for all inventories. Net realizable value is determined as the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. The Company regularly reviews inventory quantities in consideration of actual loss experiences, projected future demand, and remaining shelf life prior to sale to record a provision for excess and obsolete inventory when appropriate. The Company’s policy is to write down inventory that has become obsolete, inventory that has a cost basis in excess of its expected lower of cost or net realizable value, and inventory in excess of expected requirements. The estimate of excess quantities is judgmental and primarily dependent on the Company’s estimates of future demand for a particular product. If the estimate of future demand is too high, the Company may have to increase the reserve for excess inventory for that product and record a charge to the cost of goods sold. Other Current Assets The prepaid expenses and other current assets balance at December 31, 2020 included $4,160,000 associated with the Company's voluntary recall. The amount relates to the replacement lots and other direct costs to be received from Cordis. As of December 31, 2021, the Company has a current asset of $335,000 on its balance sheet relating to other direct costs that remain to be reimbursed from Cordis. Property and Equipment Property and equipment are recorded at cost less accumulated depreciation or amortization. Repairs and maintenance costs are expensed as incurred. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the assets, typically three years to five years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or estimated useful economic life of the asset. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in operations in the period realized. Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. If indicators of impairment exist, an impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the assets and their eventual disposition are less than their carrying amount. Impairment, if any, is measured as the amount by which the carrying amount of the long-lived assets exceeds their fair value. The Company did not record any impairment of long-lived assets during the years ended December 31, 2021, 2020 and 2019. Leases The Company accounts for its leasing arrangements in accordance with Accounting Standards Codification (“ASC”) 842, “Leases.” The Company considers if an arrangement is a lease at inception if it obtains the right to control the use of an identified asset under a leasing arrangement with an initial term greater than twelve months. The Company determines whether a contract conveys the right to control the use of an identified asset for a period of time if the contract contains both the right to obtain substantially all of the economic benefits from the use of the identified asset and the right to direct the use of the identified asset. The Company also evaluates the nature of each lease to determine whether it is an operating or financing lease and recognizes the right-of-use asset and lease liabilities based on the present value of future minimum lease payments over the expected lease term. The Company’s leases do not generally contain an implicit interest rate and therefore the Company uses the incremental borrowing rate it would expect to pay to borrow on a similar collateralized basis over a similar term in order to determine the present value of its lease payments. The Company considers renewal options in the determination of the lease term if the option to renew is reasonably certain. Variable lease costs represent payments that are dependent on usage, a rate or index. Variable lease costs, which consists primarily of taxes, insurance and common area maintenance costs, are expensed as incurred. The Company elected to account for contracts that contain lease and non-lease components as a single component, consistent with its historical practice. The Company does not have any finance leases. Redeemable Convertible Preferred Stock Warrant Liability Prior to its IPO, the Company accounted for its warrants for shares of redeemable convertible preferred stock as a liability based upon the characteristics and provisions of each instrument. Redeemable convertible preferred stock warrants classified as a liability were initially recorded at their fair value on the date of issuance and are subject to remeasurement at each subsequent balance sheet date. Any change in fair value as a result of a remeasurement was recognized as a component of other income (expense), net in the statements of operations and comprehensive loss. The Company recorded adjustments to the estimated fair value of the redeemable convertible preferred stock warrants until they were exercised. Upon their exercise, the final fair value of the warrant liability was reclassified to stockholders’ equity. Subsequent to its IPO, the Company no longer recorded any related periodic fair value adjustments. Redeemable Convertible Preferred Stock Prior to its IPO, the Company recorded its redeemable convertible preferred stock at fair value on the dates of issuance, net of issuance costs, and classified the redeemable convertible preferred stock outside of stockholders’ equity on the balance sheet as events triggering the liquidation preferences were not solely within the Company’s control. Upon the closing of the Company's IPO, all shares of convertible preferred stock then outstanding converted into an aggregate of 23,178,555 shares of common stock resulting in the reclassification of $144,140,000 from outside of stockholders’ equity to additional paid-in capital. Revenue Recognition The Company recognizes revenue in accordance with ASC Topic 606, "Revenue from Contracts with Customers." Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the Company performs the following five steps: (i)identify the contract(s) with a customer; (ii)identify the performance obligations in the contract; (iii)determine the transaction price; (iv)allocate the transaction price to the performance obligations in the contract; and (v)recognize revenue when (or as) the entity satisfies a performance obligation. As of December 31, 2021 and 2020, the Company recorded $87,000 and $71,000, respectively, of unbilled receivables, which are included in accounts receivable, net on the balance sheet, as the Company has an unconditional right to payment as of the end of the applicable period. The Company’s revenue is generated from the sale of its products to hospitals and medical centers in the United States through direct sales representatives. Revenue is recognized when obligations under the terms of a contract with customers are satisfied, which occurs with the transfer of control of the Company’s products to its customers, either upon shipment of the product or delivery of the product to the customer under the Company’s standard terms and conditions. The Company’s products are readily available for usage as soon as the customer possesses it. Upon receipt, the customer controls the economic benefits of the product, has significant risks and rewards, and the legal title. The Company has present right to payment; therefore, the transfer of control is deemed to happen at a point in time. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring the goods. For sales where the Company’s sales representative hand delivers product directly to the hospital or medical center from the sales representative’s trunk stock inventory, the Company recognizes revenue upon delivery, which represents the point in time when control transfers to the customer. Upon delivery there are legally-enforceable rights and obligations between the parties which can be identified, commercial substance exists and collectability is probable. For sales which are sent directly from the Company to hospitals and medical centers, the transfer of control occurs at the time of shipment or delivery of the product. There are no further performance obligations by the Company or the sales representative to the customer after delivery under either method of sale. As allowed under the practical expedient, the Company does not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii) contracts for which it recognizes revenue at the amount to which it has the right to invoice for services performed. The Company is entitled to the total consideration for the products ordered by customers as product pricing is fixed according to the terms of customer contracts and payment terms are short. Payment terms fall within the one-year guidance for the practical expedient which allows the Company to forgo adjustment of the promised amount of consideration for the effects of a significant financing component. The Company excludes taxes assessed by governmental authorities on revenue-producing transactions from the measurement of the transaction price. Costs associated with product sales include commissions and royalties. The Company applies the practical expedient and recognizes commissions and royalties as expense when incurred because the expense is incurred at a point in time and the amortization period is less than one year. Commissions are recorded as selling expense and royalties are recorded as cost of goods sold in the statements of operations and comprehensive loss. The Company accepts product returns at its discretion or if the product is defective as manufactured. The Company establishes estimated provisions for returns based on historical experience and considers other factors that it believes could significantly impact its expected returns, which provisions are classified within accrued liabilities on our balance sheet. The Company elected to expense shipping and handling costs as incurred and includes them in the cost of goods sold. In those cases where the Company bills shipping and handling costs to customers, it will classify the amounts billed as a component of revenue. Cost of Goods Sold The Company manufactures certain of its portfolio of TCAR products at its California facility and purchases other products from third party manufacturers. Cost of goods sold consists primarily of costs related to materials, components and sub-assemblies, manufacturing overhead costs, direct labor, reserves for excess, obsolete and non-sellable inventories as well as distribution-related expenses. A significant portion of the Company’s cost of goods sold currently consists of manufacturing overhead costs. These overhead costs include the cost of quality assurance, material procurement, inventory control, facilities, equipment and operations supervision and management. Cost of goods sold also includes depreciation expense for production equipment and certain direct costs such as shipping costs and royalties. In May 2021, the Company entered into a lease for an additional facility in Minnesota and expects to begin commercial production in the second half of 2022. During this time the Company experienced additional overhead related to manufacturing start-up and expansion of its manufacturing capacity, which were recorded as a period expense. Research and Development The Company expenses research and development costs as incurred. Research and development expenses consist primarily of engineering, product development, clinical studies to develop and support the Company’s products, regulatory expenses, medical affairs and other costs associated with products and technologies that are in development. Research and development expenses include employee compensation, including stock-based compensation, supplies, consulting, prototyping, testing, materials, travel expenses, depreciation and an allocation of facility overhead expenses. Additionally, research and development expenses include costs associated with our clinical studies including clinical trial design, clinical site reimbursement, data management, travel expenses and the cost of products used for clinical trials and internal and external costs associated with the Company’s regulatory compliance and quality assurance functions, including the costs of outside consultants and contractors that assist in the process of submitting and maintaining regulatory filings, and overhead costs. Clinical Trials The Company accrues and expenses costs for its clinical trial activities performed by third parties, including clinical research organizations and other service providers, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company determines these accruals through discussion with internal personnel and outside service providers as to progress or stage of completion of trials or services pursuant to contracts with clinical research organizations and other service providers and the agreed-upon fee to be paid for such services. Advertising Costs The Company expenses advertising costs as incurred. Advertising costs include design and production costs, including website development, physician and patient testimonial videos, written media campaigns, and other items. Advertising costs of $221,000, $194,000 and $362,000 were expensed during the years ended December 31, 2021, 2020 and 2019, respectively. Foreign Currency The Company records net gains and losses resulting from foreign exchange transactions as a component of foreign currency exchange gains or losses in other income (expense), net. The Company had no material foreign currency exchange gains or losses during the years ended December 31, 2021, 2020 and 2019. Stock–Based Compensation The Company accounts for stock-based compensation in accordance with Financial Accounting Standards Board (“FASB”) ASC 718, “Compensation-Stock Compensation.” ASC 718 requires the recognition of compensation expense, using a fair-value based method, for costs related to all share-based payments including stock options, restricted stock units and shares issued under its employee stock purchase plan. ASC 718 requires companies to estimate the fair value of all share-based payment option awards on the date of grant using an option pricing model. The fair value of stock options is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period), on a straight-line basis. For performance-based stock options, the Company will assess the probability of performance conditions being achieved in each reporting period. The amount of stock-based compensation expense recognized in any one period related to performance-based stock options can vary based on the achievement or anticipated achievement of the performance conditions. The Company accounts for option forfeitures as they occur. The Company accounts for stock-based compensation for restricted stock units at their fair value, based on the closing market price of the Company's common stock on the date of grant. These costs are recognized on a straight-line basis over the requisite service period, which is usually the vesting period. The Company accounts for stock-based compensation for its employee stock purchase plan based on the estimated fair value of the options on the date of grant. The Company estimates the grant date fair value using an option pricing model for each purchase period. These costs are recognized on a straight-line basis over the offering period. Income Taxes The Company accounts for income taxes under the liability method, whereby deferred tax assets and liabilities are determined based on the difference between the financial statements and tax bases of assets and liabilities using the enacted tax rates in effect for the year in which the differences are expected to affect taxable income. A valuation allowance is established when necessary to reduce deferred tax assets to the amounts expected to be realized. As the Company has historically incurred operating losses, it has established a full valuation allowance against its net deferred tax assets, and there is no provision for income taxes. The Company also follows the provisions of ASC 740-10, “Accounting for Uncertainty in Income Taxes.” ASC 740-10 prescribes a comprehensive model for the recognition, measurement, presentation and disclosure in financial statements of any uncertain tax positions that have been taken or expected to be taken on a tax return. No liability related to uncertain tax positions is recorded on the financial statements. It is the Company’s policy to include penalties and interest expense related to income taxes as part of the provision for income taxes. Comprehensive Loss Comprehensive loss consists of net loss and changes in unrealized gains and losses on investments classified as available-for-sale. For the years ended December 31, 2021, 2020 and 2019, the Company’s unrealized gains and losses on available-for-sale investments represent the only component of other comprehensive loss that are excluded from the reported net loss and that are presented in the statements of operations and comprehensive income. Accumulated other comprehensive loss is presented in the accompanying balance sheets as a component of stockholders' equity. Net Loss per Share Basic net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration for potential dilutive common shares. Diluted net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, redeemable convertible preferred stock and warrants, common stock options, and restricted stock units are considered to be potentially dilutive securities. Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share as the inclusion of all potential dilutive common shares would have been anti-dilutive. The Company allocates no loss to participating securities because they have no contractual obligation to share in the losses of the Company. The shares of the Company’s redeemable convertible preferred stock participate in any dividends declared by the Company and are therefore considered to be participating securities. Net loss per share was determined as follows (in thousands, except share and per share data): Year Ended December 31, 2021 2020 2019Net loss $ (49,811) $ (47,365) $ (52,415)Weighted average common stock outstanding used to compute net loss per share, basic and diluted 34,635,358 32,965,539 22,956,679Net loss per share, basic and diluted $ (1.44) $ (1.44) $ (2.28) The following potentially dilutive securities outstanding have been excluded from the computation of diluted weighted average shares outstanding because such securities have an antidilutive impact due to the Company’s net loss: December 31, 2021 2020 2019Common stock options 3,780,939 4,237,828 4,310,790Restricted stock units 530,274 68,396 —Total 4,311,213 4,306,224 4,310,790 Segment and Geographical Information The Company operates and manages its business as one reportable and operating segment. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. Primarily all of the Company’s long-lived assets are based in the United States. Long-lived assets are comprised of property and equipment. All of the Company’s revenue was in the United States for the years ended December 31, 2021, 2020 and 2019, based on the shipping location of the external customer.

Fair Value Measurements (Tables)	12 Months Ended
Fair Value Measurements (Tables)	Dec. 31, 2021
Fair Value Measurements [Abstract]
Financial Liabilities Measure on a Recurring Basis	December 31, 2021 Level 1 Level 2 Level 3 TotalAssets: Money market funds$ 21,062 $— $— $ 21,062 $ 21,062 $ — $— $ 21,062 December 31, 2020 Level 1 Level 2 Level 3 TotalAssets: Money market funds$ 60,295 $— $— $ 60,295Commercial paper — 39,577 — 39,577Corporate bonds/notes — 7,969 — 7,969U.S. government securities — 38,470 — 38,470 $ 60,295 $ 86,016 $— $ 146,311

Debt - Stifel Bank (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
Debt - Stifel Bank (Narrative) (Details) - USD ($)	Oct. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Jan. 15, 2021
Subsequent Event [Line Items]
Prepayment premium fee			$ 2,496,000
Loss on debt extinguishment			$ (1,119,000)
Stifel Bank [Member]
Subsequent Event [Line Items]
Aggregate outstanding principal balance		$ 49,000,000
Annual interest rate		4.75%
Proceeds from debt	$ 49,000,000
Percent of original principal threshold		0.75%
Redemption amount		$ 375,000
Stated interest rate		4.75%
Debt, Covenant, Unrestricted Cash				$ 20,000,000
Debt, Covenant, Revenue Covenant				$ 60,000,000
Prime Rate [Member] \| Stifel Bank [Member]
Subsequent Event [Line Items]
Variable interest rate		0.75%
Term Loan [Member]
Subsequent Event [Line Items]
Debt pay off	46,674,000
Prepayment premium fee	305,000
Debt interest	365,000
Facility fee	2,191,000
Loss on debt extinguishment	$ 1,119,000
Term Loan [Member] \| Stifel Bank [Member]
Subsequent Event [Line Items]
Facility amount		$ 50,000,000
Secured Revolving Credit Facility [Member] \| Secured Debt [Member] \| Stifel Bank [Member]
Subsequent Event [Line Items]
Facility amount		50,000,000
Secured Revolving Credit Facility, Subfacility [Member] \| Term Loan [Member] \| Stifel Bank [Member]
Subsequent Event [Line Items]
Facility amount		2,000,000
Loan Agreement [Member]
Subsequent Event [Line Items]
Facility amount		50,000,000
Loan Agreement [Member] \| Stifel Bank [Member]
Subsequent Event [Line Items]
Facility amount		$ 50,000,000
Stated interest rate		4.75%
Loan Agreement [Member] \| Prime Rate [Member] \| Stifel Bank [Member]
Subsequent Event [Line Items]
Variable interest rate		0.50%

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	Year Ended December 31, 2021 2020 2019United States $ (49,811) $ (47,365) $ (52,415)International — — — $ (49,811) $ (47,365) $ (52,415)
Schedule of Effective Income Tax Rate Reconciliation	Year Ended December 31, 2021 2020 2019Tax at federal statutory rate $ (10,460) $ (9,947) $ (11,007)State taxes, net of federal benefit (1,852) (1,958) (2,270)Permanent differences (5,224) (8,489) (4,731)Loss on Series C warrant liability — — 5,330Change in valuation allowance 17,918 22,164 12,797General business credits (852) (1,268) (319)Other 490 (491) 208 Provision for income taxes $ 20 $ 11 $ 8
Schedule of Deferred Tax Assets and Liabilities	December 31, 2021 2020Deferred tax assets: Net operating loss carryforwards $ 77,616 $ 63,069 Research and development credits 7,732 7,191 Capitalized start-up costs/Intangibles 4 8 Accruals and reserves 2,301 2,337 Stock-based compensation 4,392 1,859 Operating lease liability 1,751 935 Interest limitation 1,314 813Total deferred tax assets 95,110 76,212Less: Valuation allowance (93,207) (75,289)Deferred tax liabilities: Operating lease asset (1,297) (707) Property and equipment (606) (216)Total deferred tax liabilities (1,903) (923)Net deferred tax assets $ — $—
Reconciliation of Unrecognized Tax Benefits	December 31, 2021 2020 2019Balance at the beginning of year $ 2,019 $ 1,436 $ 1,348Increases related to current years’ tax positions 704 342 88Increases related to prior years’ tax positions 591 241 —Balance at end of year $ 3,314 $ 2,019 $ 1,436

Balance Sheet Components (Schedule of Inventory) (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Components [Abstract]
Raw materials	$ 2,447,000	$ 1,785,000
Finished products	15,437,000	10,599,000
Inventory, gross	17,884,000	12,384,000
Less: Reserve for excess and obsolete	(33,000)	(2,395,000)
Inventories	17,851,000	9,989,000
Inventory, Work in Process, Gross	0	0
Excess And Obsolete Inventory, Reserve	$ 1,000	$ 2,377,000

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2021
Commitments and Contingencies [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Operating Lease and Rights of Use The Company’s operating lease obligation at its corporate headquarters in California consists of leased office, laboratory, and manufacturing space under a non-cancellable operating lease that expires in October 2024. The lease agreement includes a renewal provision allowing the Company to extend this lease for an additional period of five years. In May 2021, the Company entered into a new, non-cancelable operating lease for additional office, laboratory and manufacturing space in Minnesota that expires in November 2029. The lease agreement includes a renewal provision allowing the Company to extend this lease for two additional five year terms. In connection with the lease, the Company recognized a right-of-use asset and lease liability of $3,307,000. Operating lease costs were $1,234,000 for the year ended December 31, 2021 and $870,000 for each of the years ended December 31, 2020 and 2019. Cash paid (net of tenant improvement allowances received) for amounts included in the measurement of operating lease liabilities was $(34,000), $769,000 and $721,000 for the years ended December 31, 2021, 2020 and 2019, respectively. As of December 31, 2021, the weighted average discount rate was approximately 6.50% and the weighted average remaining lease term was 5.86 years. As of December 31, 2020, the weighted average discount rate was approximately 6.50% and the weighted average remaining lease term was 3.83 years. Balance sheet information as of December 31, 2021 consists of the following (in thousands): December 31,Operating Lease: 2021 2020Operating lease right-of-use asset in other non-current assets $ 5,219 $ 2,798Operating lease liability in accrued liabilities $ 1,294 $ 850Operating lease liability in other liabilities 5,747 2,850Total operating lease liabilities $ 7,041 $ 3,700 The following table summarizes the Company's operating lease maturities as of December 31, 2021 (in thousands): Year Ending December 31: Amount2022 $ 6202023 1,9672024 1,7642025 8822026 904Thereafter 2,769Total lease payments 8,906Less: imputed interest (1,865)Present value of lease liabilities $ 7,041 Purchase Obligations Purchase obligations consist of agreements to purchase goods and services entered into in the ordinary course of business. As of December 31, 2021, the Company had non-cancellable purchase obligations to suppliers of $5,661,000. Indemnification In the normal course of business, the Company enters into contracts and agreements with suppliers and other parties that contain a variety of representations and warranties and may provide for indemnification of the counterparty. The Company’s exposure under these agreements is unknown because it involves claims that may be made against it in the future but have not yet been made. To date, the Company has not been subject to any claims or been required to defend any action related to its indemnification obligations. The Company indemnifies each of its directors and officers for certain events or occurrences, subject to certain limits, while the director is or was serving at the Company’s request in such capacity, as permitted under Delaware law and in accordance with its certificate of incorporation and bylaws. The term of the indemnification period lasts as long as a director may be subject to any proceeding arising out of acts or omissions of such director in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director liability insurance. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, the Company has not recognized any liabilities relating to these obligations as of December 31, 2021. Contingencies The Company is not involved in any pending legal proceedings that it believes could have a material adverse effect on its financial condition, results of operations or cash flows. From time to time, the Company may pursue litigation to assert its legal right and such litigation may be costly and divert the efforts and attention of its management and technical personnel which could adversely affect its business. The Company accrues a liability for such matters when it is probable that future expenditures will be made, and such expenditures can be reasonably estimated. There were no contingent liabilities requiring accrual at December 31, 2021 and 2020.

Stock Option Plans	12 Months Ended
Stock Option Plans	Dec. 31, 2021
Stock Option Plans [Abstract]
Stock Option Plans	10. Stock Option Plans In 2007, the Company established its 2007 Stock Option Plan which provided for the granting of stock options to employees, directors and consultants of the Company. In connection with its acquisition of NeuroCo in December 2018, the Company also assumed NeuroCo’s 2015 Equity Incentive Plan. In March 2019, the Company's Board of Directors approved the termination of the 2007 Stock Option Plan and the NeuroCo 2015 Equity Incentive Plan and the adoption of the 2019 Equity Incentive Plan, or the 2019 Plan, which became effective immediately prior to the Company's IPO. The 2019 Plan provides for the grant of ISOs to employees and for the grant of NSOs, restricted stock, restricted stock units, stock appreciation rights, performance units and performance shares to employees, directors and consultants. A total of 2,317,000 shares of common stock were initially reserved for issuance pursuant to the 2019 Plan. In addition, the shares reserved for issuance under the 2019 Plan will also include shares reserved but not issued under the 2007 Stock Option Plan, plus any share awards granted under the 2007 Stock Option Plan that expire or terminate without having been exercised in full or that are forfeited or repurchased. In addition, the number of shares available for issuance under the 2019 Plan will also include an annual increase on the first day of each fiscal year, equal to the lesser of (i) 3,000,000 shares; (ii) 4.0% of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year; or (iii) an amount as determined by the Board of Directors. As of December 31, 2021, the Company has reserved 5,016,420 shares of common stock for issuance under the 2019 Plan. A summary of the shares available for issuance under the 2007 Stock Option Plan, NeuroCo 2015 Equity Incentive Plan and 2019 Plan, or the Plans, is as follows: Number of SharesBalances, December 31, 2018 57,889Authorized 2,317,000Granted (848,023)Canceled 27,824Balances, December 31, 2019 1,554,690Authorized 1,250,210Granted/Awarded (1,079,883)Cancelled 65,670Balances, December 31, 2020 1,790,687Authorized 1,369,985Granted/Awarded (847,080)Cancelled 163,620Balances, December 31, 2021 2,477,212 The exercise price of ISOs and NSOs shall not be less than 100% and 85%, respectively, of the estimated fair value of the shares on the date of grant as determined by the Board of Directors. The exercise price of ISOs and NSOs granted to a 10% stockholder shall not be less than 110% of the estimated fair value of the shares on the date of grant as determined by the Board of Directors. To date, options have a term of ten years and generally vest over 4 years from the date of grant. Stock option activity under the Company's Plans is set forth below: Options Outstanding Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in Years) Aggregate Intrinsic Value (in thousands)Balances, December 31, 2018 4,364,377 $3.79 7.36 $33,132 Options granted 848,023 $22.77 Options exercised (873,786) $1.77 Options cancelled (27,824) $8.71 Balances, December 31, 2019 4,310,790 $7.91 7.27 $140,234 Options granted 1,010,843 $40.67 Options exercised (1,018,779) $3.42 Options cancelled (65,026) $23.32 Balances, December 31, 2020 4,237,828 $16.56 7.38 $197,407 Options granted 323,057 $ 53.94 Options exercised (643,507) $ 7.49 Options cancelled (136,439) $ 40.30 Balances, December 31, 2021 3,780,939 $ 20.45 6.71 $ 91,900Vested and exercisable at December 31, 2021 2,732,674 $ 13.64 6.13 $ 81,395Vested and expected to vest at December 31, 2021 3,780,939 $ 20.45 6.71 $ 91,900 The aggregate intrinsic value of options exercised during the years ended December 31, 2021, 2020 and 2019 was $29,355,000, $47,861,000 and $24,867,000, respectively. The aggregate intrinsic value was calculated as the difference between the exercise prices of the underlying options and the estimated fair value of the common stock on the date of exercise. The weighted-average grant date fair value of options granted during the years ended December 31, 2021, 2020 and 2019 was $23.83, $18.22 and $10.17 per share, respectively. The total fair value of options vested during the years ended December 31, 2021, 2020 and 2019 was $9,076,000, $5,138,000 and $2,221,000, respectively, based on the grant date fair value. The following table summarizes information about stock options outstanding and vested as of December 31, 2021: Options Outstanding Options VestedExercise Price Options Outstanding Weighted Average Remaining Contractual Term (in Years) Weighted Average Exercise Price Number Exercisable Weighted Average Exercise Price$1.35 - $3.16 868,256 4.58 $ 2.05 868,256 $ 2.05$4.73 - $7.10 577,759 6.17 $ 5.74 542,305 $ 5.71$8.27 - $12.41 490,391 6.06 $ 11.74 470,037 $ 11.83$20.00 - $30.00 616,871 7.26 $ 20.00 400,815 $ 20.00$30.93 - $46.40 682,913 8.12 $ 33.60 308,065 $ 34.34$47.20 - $70.80 544,749 8.86 $ 57.22 143,196 $ 57.48 3,780,939 6.71 $ 20.45 2,732,674 $ 13.64 Restricted Stock Units In March 2020, the Company began granting restricted stock units, or RSUs, under the 2019 Plan. RSUs generally vest over four years in annual equal increments. The total grant date fair value of awards granted during the year ended December 31, 2021 and 2020 was $28,110,000 and $3,186,000, respectively. The total fair value of awards vested during the year ended December 31, 2021 was $1,893,000. No awards vested during the year ended December 31, 2020. The fair value of RSUs is based on the Company’s closing stock price on the date of grant. A summary of RSUs activity for the years ended December 31, 2021 and 2020 is as follows: Number of Restricted Stock Units Weighted Average Grant Date Fair ValueBalances, December 31, 2019 — $ —Restricted stock granted 69,040 $ 46.14Restricted stock vested — $ —Restricted stock forfeited (644) $ 44.62Balances, December 31, 2020 68,396 $ 46.16Restricted stock granted 524,023 $ 53.64Restricted stock vested (34,964) $ 49.95Restricted stock forfeited (27,181) $ 51.99Balances, December 31, 2021 530,274 $ 53.01Expected to vest at December 31, 2021 530,274 $ 53.01 2019 Employee Stock Purchase Plan In March 2019, the Company's Board of Directors adopted the 2019 Employee Stock Purchase Plan, or the 2019 ESPP, under which eligible employees are permitted to purchase common stock at a discount through payroll deductions. A total of 434,000 shares of common stock were initially reserved for issuance and is increased on the first day of each fiscal year by an amount equal to the lesser of (i) 1,200,000 shares (ii) 1.0% of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year; or (iii) an amount as determined by the Board of Directors. As of December 31, 2021, the Company has reserved 1,089,048 shares of common stock for issuance under the 2019 ESPP. The price of the common stock purchased will be the lower of 85% of the fair market value of the common stock at the beginning of an offering period or at the end of a purchase period. The 2019 ESPP was effective upon adoption by the Company's Board of Directors but was not in use until the completion of the Company's IPO in April 2019. The 2019 ESPP is intended to qualify as an "employee stock purchase plan" within the meaning of Section 423 of the Internal Revenue Code of 1986, as amended. As of December 31, 2021, 166,951 shares of common stock have been issued to employees participating in the 2019 ESPP and 922,097 shares were available for future issuance under the 2019 ESPP. Stock-Based Compensation The Company estimated the fair value of stock options using the Black–Scholes option pricing model. The fair value of employee and nonemployee stock options is being amortized on a straight–line basis over the requisite service period of the awards. The fair value of employee and nonemployee stock options was estimated using the following assumptions for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019Expected term (in years) 5.25 - 6.25 5.00 - 6.25 5.00 - 6.25Expected volatility 45.0% - 50.4% 43.0% - 50.3% 42.4% - 42.9%Risk-free interest rate 0.41% - 1.08% 0.32% - 1.41% 1.47% - 2.54%Dividend yield —% —% —% Prior to completion of the Company's IPO in April 2019, the fair value of common stock was determined by the Company’s Board of Directors, who considered, among other things, contemporaneous valuations of the Company’s common stock prepared by an unrelated third-party valuation firm in accordance with the guidance provided by the American Institute of Certified Public Accountants Practice Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. For stock options granted after the completion of the IPO, the fair value of the underlying common stock is based on the closing price of the Company's common stock on The NASDAQ Global Market on the date of grant. The expected term of stock options represents the weighted-average period the stock options are expected to remain outstanding. The Company does not have sufficient historical exercise and post-vesting termination activity to provide accurate data for estimating the expected term of options and has opted to use the “simplified method,” whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option. The expected stock price volatility assumption was determined by supplementing its historical stock trading volatility with the historical volatilities for industry peers, as the Company does not have sufficient trading history for the Company’s common stock. The Company will continue to analyze the historical stock price volatility and expected term assumption as more historical data for the Company’s common stock becomes available. The risk-free interest rate assumption is based on the U.S. Treasury instruments whose term was consistent with the expected term of the Company’s stock options. The expected dividend assumption is based on the Company’s history and expectation of dividend payouts. The Company has elected to recognize forfeitures of share-based payment awards as they occur. The fair value of the shares to be issued under the Company’s 2019 ESPP was estimated using the Black-Scholes valuation model with the following assumptions for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019Expected term (in years) 0.50 0.50 0.50 - 0.63Expected volatility 46.9% - 51.6% 44.4% - 76.4% 44.4% - 47.8%Risk-free interest rate 0.03% - 0.10% 0.10% - 1.58% 1.58% - 2.45%Dividend yield —% —% —% The following table summarizes the total stock-based compensation expense included in the statements of operations for all periods presented (in thousands): Year Ended December 31, 2021 2020 2019 Cost of goods sold$ 635 $ 339 $ 179Research and development expenses 2,909 1,110 426Selling, general and administrative expenses 11,068 5,777 2,372 $ 14,612 $ 7,226 $ 2,977 As of December 31, 2021, there was total unrecognized compensation costs of $16,737,000 related to stock options expected to be recognized over a period of approximately 2.37 years, a total of $24,183,000 of unrecognized compensation costs related to unvested RSUs expected to be recognized over a period of approximately 3.32 years and $365,000 related to the ESPP, which the Company will recognize over 0.38 years.

Commitments and Contingencies (Tables)	12 Months Ended
Commitments and Contingencies (Tables)	Dec. 31, 2021
Commitments and Contingencies [Abstract]
Balance Sheet Information	December 31,Operating Lease: 2021 2020Operating lease right-of-use asset in other non-current assets $ 5,219 $ 2,798Operating lease liability in accrued liabilities $ 1,294 $ 850Operating lease liability in other liabilities 5,747 2,850Total operating lease liabilities $ 7,041 $ 3,700
Operating Lease Maturities	Year Ending December 31: Amount2022 $ 6202023 1,9672024 1,7642025 8822026 904Thereafter 2,769Total lease payments 8,906Less: imputed interest (1,865)Present value of lease liabilities $ 7,041

Balance Sheet Components	12 Months Ended
Balance Sheet Components	Dec. 31, 2021
Balance Sheet Components [Abstract]
Balance Sheet Components	5. Balance Sheet Components Investments The Company’s cash equivalents consists of $21,062,000 in money market funds as of December 31, 2021 and approximates fair value. The Company had no investments as of December 31, 2021. The fair value of the Company's available-for-sale investments as of December 31, 2020 are as follows (in thousands): December 31, 2020 Gross Unrealized Estimated Amortized Cost Gains Losses Fair ValueMoney market funds$ 60,295 $— $— $ 60,295Commercial paper 39,577 — — 39,577Corporate bonds/notes 7,970 — (1) 7,969U.S. government securities 38,430 42 (2) 38,470 $ 146,272 $ 42 $ (3) $ 146,311 Classified as: Cash equivalents $ 68,295Short-term investments 78,016 $ 146,311 The following table summarizes the fair value of the Company’s cash equivalents and available-for-sale investments classified by maturity as of December 31, 2021 and 2020 (in thousands): December 31,‎2021 December 31,‎2020Amounts maturing within one year $ 21,062 $ 146,311Amounts maturing after one year through two years — — $ 21,062 $ 146,311 The following table presents the Company's available-for-sale investments that were in an unrealized loss position as of December 31, 2020 (in thousands): December 31, 2020 Less than 12 monthsAssets: Fair Value Unrealized LossCorporate bonds/notes $ 5,369 $ (1)U.S. government securities 10,128 (2) $ 15,497 $ (3) Inventories Components of inventories were as follows (in thousands): December 31, 2021 2020Raw materials $ 2,447 $ 1,785Finished products 15,437 10,599 17,884 12,384Less: Reserve for excess and obsolete (33) (2,395) $ 17,851 $ 9,989 As of December 31, 2021 and 2020, there were no work-in-process inventories. The reserve for excess and obsolete inventory at December 31, 2021 and 2020 included $1,000 and $2,377,000, respectively, associated with the Company's voluntary product recall. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): December 31, 2021 2020Furniture and fixtures$ 1,005 $ 726Equipment 2,945 1,699Software 284 226Leasehold improvements 2,050 2,043 6,284 4,694Less: Accumulated depreciation (3,330) (2,332)Add: Construction-in-progress 4,743 482 $ 7,697 $ 2,844 Depreciation and amortization expense was $1,032,000, $789,000 and $712,000 for the years ended December 31, 2021, 2020 and 2019, respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): December 31, 2021 2020Accrued payroll and related expenses $ 13,898 $ 9,573Provision for sales returns 359 820Accrued professional services 2,039 2,520Recall replacement obligation 11 1,696Operating lease liability 1,294 850Accrued royalty expense 687 518Deferred revenue 157 206Accrued travel expenses 590 237Accrued clinical expenses 99 113Accrued other expenses 668 424 $ 19,802 $ 16,957

Debt	12 Months Ended
Debt	Dec. 31, 2021
Debt [Abstract]
Debt	6. Debt CRG In October 2015, the Company entered into a term loan agreement with CRG. The term loan agreement provides for up to $30,000,000 in term loans split into two tranches as follows: (i) the Tranche A Loans provided for $20,000,000 in term loans, and (ii) the Tranche B Loans provided for up to $10,000,000 in term loans. The Company drew down the Tranche A Loans on October 13, 2015. The Tranche B Loans were available to be drawn prior to March 29, 2017. In January 2017, the term loan agreement was amended to extend the commitment period of the Tranche B Loans to April 28, 2017. In April 2017, the Company drew down $5,000,000 of the available Tranche B Loans. In September 2018, the term loan agreement was amended to provide for additional term loans in an aggregate principal amount of up to $25,000,000. In September 2018, the Company drew down an additional $15,000,000 under the amended term loan agreement with CRG, no additional draw was taken. Under the terms of the amended term loan agreement, the related fixed interest rate was 10.0%, 8.0% of the interest was due and payable in cash and at the election of the Company, 2.0% of the interest due and payable may be "paid in kind". All unpaid principal, and accrued and unpaid interest, was due and payable in full on December 31, 2022. On October 29, 2020, in connection with the consummation of the Loan and Security agreement with Stifel Bank as noted below, the Company repaid all amounts outstanding under the term loan with CRG. Stifel Bank In October 2020, the Company entered into a Loan and Security Agreement, or Loan Agreement, with Stifel Bank which provides for a $50,000,000 loan facility, comprised of a $50,000,000 secured revolving credit facility, with a $2,000,000 subfacility for the issuance of letters of credit and other ancillary banking services, and a $50,000,000 secured term loan facility, provided that amounts outstanding under both facilities may not exceed an aggregate principal amount of $50,000,000 at any time. Any borrowings under the revolving loan facility mature on October 29, 2022, or October 29, 2023 if as of October 29, 2022, no event of default has occurred and we are in compliance with the terms of the Loan Agreement. Borrowings under the term loan facility mature on October 29, 2024. Interest under the revolving credit facility is the greater of a) 0.5% above the "Prime Rate" as published by The Wall Street Journal or b) 4.75%. Also in October 2020, the Company drew down $49,000,000 under the term loan facility and used the majority of the proceeds to pay off and terminate the prior term loan agreement with CRG totaling $46,674,000, which included a prepayment premium of $305,000, a final interest payment of $365,000 and a facility fee of $2,191,000. The Company recognized a loss on debt extinguishment of $1,119,000 in connection with the early termination of the term loan agreement with CRG. The principal amount of outstanding term loans under the Loan Agreement with Stifel Bank shall be repaid in equal monthly installments beginning on November 29, 2022. Interest under the term loan facility is the greater of a) 0.75% above the "Prime Rate" as published by The Wall Street Journal or b) 4.75%. The term loan may not be reborrowed once repaid, but the Company may prepay the term loan at any time without premium or penalty. The Company also concurrently entered in a Success Fee Agreement in October 2020 with Stifel Bank, which requires that the Company pay Stifel Bank the lesser of 0.75% of the original principal amount of all credit extensions made under the Loan Agreement or $375,000 in the event the Company completes a Liquidity Event (liquidation, merger, sale of the Company or change in control). The Success Fee Agreement terminates on October 29, 2025. The Company has determined the probability of a Liquidity Event to be remote and accordingly, has not recognized a liability as of December 31, 2021. Obligations under the Loan Agreement are secured by substantially all of the Company's assets. Beginning on January 15, 2021, the Loan Agreement requires that the Company maintain unrestricted cash and cash equivalents with Stifel Bank or at Stifel Bank Affiliates of at least $20,000,000. In addition, for any fiscal quarter where the Company's unrestricted cash and cash equivalents maintained with Stifel Bank or at Stifel Bank Affiliates are less than $60,000,000 for any day during such fiscal quarter, the Company must comply with a minimum revenue covenant. Additionally, the Loan Agreement contains customary affirmative and negative covenants, including covenants limiting the Company's ability and the ability of the Company's subsidiaries to, among other things, dispose of assets, effect certain mergers, incur debt, grant liens, pay dividends and distributions on capital stock, make investments and acquisitions, and enter into transactions with affiliates, in each case subject to customary exceptions for a loan facility of this size and type. The events of default under the Loan Agreement include, among others, payment defaults, material misrepresentations, breaches of covenants, cross defaults with certain other material indebtedness, bankruptcy and insolvency events, and judgment defaults. The occurrence of an event of default could result in the acceleration of our obligations under the Loan Agreement, the termination of the lender’s commitments, a 5% increase in the applicable rate of interest and the exercise by the lender of other rights and remedies provided for under the Loan Agreement. As of December 31, 2021, the aggregate outstanding principal balance under the Loan Agreement was $49,000,000 and the annual interest rate was 4.75%. As of December 31, 2021, the Company was in compliance with all applicable financial covenants. As of December 31, 2021, management does not believe that it is probable that the above events of default will be triggered within the next twelve months, therefore, the debt is classified as short or long-term on the balance sheet based on its future maturities. Future maturities under the Stifel Bank term loan agreement as of December 31, 2021 are as follows (in thousands): Year Ending December 31: Amount2022 $ 6,2572023 25,7492024 21,457 53,463Less: Amount representing interest (4,463)Less: Amount representing debt discount and debt issuance costs (309)Present value of minimum payments $ 48,691

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning of year	$ 2,019	$ 1,436	$ 1,348
Increases related to current years’ tax positions	704	342	88
Increases related to prior years’ tax positions	591	241
Balance at end of year	$ 3,314	$ 2,019	$ 1,436

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 110,231	$ 69,466
Short-term investments		78,016
Accounts receivable, net of allowances of $6 and $13 at December 31, 2021 and December 31, 2020, respectively	11,832	9,070
Inventories	17,851	9,989
Prepaid expenses and other current assets	3,412	6,787
Total current assets	143,326	173,328
Property and equipment, net	7,697	2,844
Restricted cash	232	310
Other non-current assets	5,370	2,832
Total assets	156,625	179,314
Current liabilities:
Accounts payable	2,379	2,598
Accrued liabilities	19,802	16,957
Short-term Debt	3,905
Total current liabilities	26,086	19,555
Long-term debt	44,786	48,533
Other liabilities	6,513	3,726
Total liabilities	77,385	71,814
Commitments and contingencies (Note 7)
Stockholders’ equity):
Preferred stock, $0.001 par value Shares authorized: 5,000,000 at December 31, 2021 and 2020 Shares issued and outstanding: none at December 31, 2021 and 2020
Common stock, $0.001 par value Shares authorized: 100,000,000 at December 31, 2021 and 2020 Shares issued and outstanding: 34,980,896 and 34,249,649 at December 31, 2021 and 2020, respectively	35	34
Additional paid-in capital	367,907	346,318
Accumulated other comprehensive income		39
Accumulated deficit	(288,702)	(238,891)
Total stockholders’ equity	79,240	107,500
Total liabilities and stockholders’ equity	$ 156,625	$ 179,314

401(k) Plan (Details) - USD ($) $ in Thousands	12 Months Ended
401(k) Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
401(k) Plan [Abstract]
Percentage employee contribution	90.00%
Employer discretionary contribution	$ 1,313	$ 959
Employer contribution match percentage	50.00%
Percent of matching contribution of the employee's pay	5.00%

Debt - CRG (Narrative) (Details) - Term Loan [Member] - USD ($)	1 Months Ended		36 Months Ended
	Sep. 30, 2018	Apr. 30, 2017	Dec. 31, 2021
Term Loan, Tranche A And B [Member]
Debt Instrument [Line Items]
Debt, face amount			$ 30,000,000
Term Loan, Tranche A [Member]
Debt Instrument [Line Items]
Debt, face amount			20,000,000
Term Loan, Tranche B [Member]
Debt Instrument [Line Items]
Debt, face amount			10,000,000
Proceeds from debt		$ 5,000,000
Term Loan, Additional [Member]
Debt Instrument [Line Items]
Debt, face amount			25,000,000
Proceeds from debt	$ 15,000,000		$ 0
Stated interest rate			10.00%
Interest rate paid-in-kind			8.00%
Interest rate paid in cash			2.00%

Debt (Future Maturities Under the Term Loan) (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Debt [Abstract]
2022	$ 6,257
2023	25,749
2024	21,457
Long-term debt, gross before accretion of closing fees	53,463
Less: Amount representing interest	(4,463)
Less: Amount representing debt discount and debt issuance costs	(309)
Present value of minimum payments	$ 48,691

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References + Details

Stockholders' Equity (Details) - USD ($)	12 Months Ended
Stockholders' Equity (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Stockholders' Equity (Deficit) [Abstract]
Preferred shares authorized (in shares)	5,000,000	5,000,000
Preferred shares (in USD per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	100,000,000	100,000,000
Par value (in USD per share)	$ 0.001	$ 0.001
Shares issued (in shares)	34,980,896	34,249,649
Shares outstanding (in shares)	34,980,896	34,249,649
Dividends declared	$ 0
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 20.00
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	5,968
Warrants outstanding (in shares)	0	0
Stockholder Short Swing Profits	$ 32,000

Stock Option Plans (Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Beginning balance (in shares)	4,237,828	4,310,790	4,364,377
Options granted (in shares)	323,057	1,010,843	848,023
Options exercised (in shares)	(643,507)	(1,018,779)	(873,786)
Options cancelled (in shares)	(136,439)	(65,026)	(27,824)
Ending balance (in shares)	3,780,939	4,237,828	4,310,790	4,364,377
Vested and exercisable (in shares)	2,732,674
Vested and expect to vest (in shares)	3,780,939
Weighted Average Exercise Price
Beginning balance (in USD per share)	$ 16.56	$ 7.91	$ 3.79
Options granted (in USD per share)	53.94	40.67	22.77
Options exercised (in USD per share)	7.49	3.42	1.77
Options cancelled (in USD per share)	40.30	23.32	8.71
Ending balance (in USD per share)	20.45	$ 16.56	$ 7.91	$ 3.79
Vested and exercisable (in USD per share)	13.64
Vested and expected to vest (in USD per share)	$ 20.45
Weighted Average Remaining Contractual Term (in Years)
Awards outstanding	6 years 8 months 15 days	7 years 4 months 17 days	7 years 3 months 7 days	7 years 4 months 9 days
Vested and exercisable	6 years 1 month 17 days
Vested and expected to vest	6 years 8 months 15 days
Aggregate Intrinsic Value (in thousands)
Awards outstanding	$ 91,900	$ 197,407	$ 140,234	$ 33,132
Vested and exercisable	81,395
Vested and expected to vest	$ 91,900

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Allowances for accounts receivables	$ 6	$ 13
Preferred stock, $0.001 par value
Preferred shares (in USD per share)	$ 0.001	$ 0.001
Preferred shares authorized (in shares)	5,000,000	5,000,000
Common stock, $0.001 par value
Common stock, par value (in USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	34,980,896	34,249,649
Shares outstanding (in shares)	34,980,896	34,249,649

Income Taxes - Reconciliation of U.S Statutory Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Tax at federal statutory rate	$ (10,460)	$ (9,947)	$ (11,007)
State taxes, net of federal benefit	(1,852)	(1,958)	(2,270)
Permanent differences	(5,224)	(8,489)	(4,731)
Loss on Series C warrant liability			5,330
Change in valuation allowance	17,918	22,164	12,797
General business credits	(852)	(1,268)	(319)
Other	490	(491)	208
Provision for income taxes	$ 20	$ 11	$ 8

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statements of Operations and Comprehensive Loss [Abstract]
Revenue	$ 101,475	$ 75,227	$ 63,354
Cost of goods sold	25,446	21,291	15,927
Gross profit	76,029	53,936	47,427
Operating expenses:
Research and development	27,110	21,271	12,272
Selling, general and administrative	96,387	75,524	63,220
Total operating expenses	123,497	96,795	75,492
Loss from operations	(47,468)	(42,859)	(28,065)
Interest income	198	1,104	1,656
Interest expense	(2,518)	(4,411)	(4,952)
Loss on debt extinguishment		(1,119)
Other income (expense), net	(23)	(80)	(21,054)
Net loss	(49,811)	(47,365)	(52,415)
Other comprehensive loss:
Change in unrealized gain (loss) on investments, net	(39)	37	2
Net change in other comprehensive loss	(39)	37	2
Net loss and comprehensive loss	$ (49,850)	$ (47,328)	$ (52,413)
Net loss per share, basic and diluted	$ (1.44)	$ (1.44)	$ (2.28)
Weighted average common shares used to compute net loss per share, basic and diluted	34,635,358	32,965,539	22,956,679

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes The components of income before taxes are as follows (in thousands): Year Ended December 31, 2021 2020 2019United States $ (49,811) $ (47,365) $ (52,415)International — — — $ (49,811) $ (47,365) $ (52,415) A reconciliation of the statutory U.S. federal rate to the Company’s effective tax rate is as follows (in thousands): Year Ended December 31, 2021 2020 2019Tax at federal statutory rate $ (10,460) $ (9,947) $ (11,007)State taxes, net of federal benefit (1,852) (1,958) (2,270)Permanent differences (5,224) (8,489) (4,731)Loss on Series C warrant liability — — 5,330Change in valuation allowance 17,918 22,164 12,797General business credits (852) (1,268) (319)Other 490 (491) 208 Provision for income taxes $ 20 $ 11 $ 8 The Company's provision for income taxes amounts are included within other income (expense) on the statements of operations and comprehensive loss. Significant components of the Company’s net deferred tax assets as of December 31, 2021 and 2020 consist of the following (in thousands): December 31, 2021 2020Deferred tax assets: Net operating loss carryforwards $ 77,616 $ 63,069 Research and development credits 7,732 7,191 Capitalized start-up costs/Intangibles 4 8 Accruals and reserves 2,301 2,337 Stock-based compensation 4,392 1,859 Operating lease liability 1,751 935 Interest limitation 1,314 813Total deferred tax assets 95,110 76,212Less: Valuation allowance (93,207) (75,289)Deferred tax liabilities: Operating lease asset (1,297) (707) Property and equipment (606) (216)Total deferred tax liabilities (1,903) (923)Net deferred tax assets $ — $— In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management believes it is more likely than not that the deferred tax assets will not be realized; accordingly, a valuation allowance has been established on U.S. net deferred tax assets. The valuation allowance increased $17,918,000 during the year ended December 31, 2021 and increased by $22,163,000 during the year ended December 31, 2020. As of December 31, 2021, the Company had net operating loss carryforwards of approximately $301,306,000 and $254,476,000 for federal and state income tax purposes, respectively. The federal and state net operating loss carryforwards begin to expire in 2027 and 2028, respectively. Federal NOL carryforwards generated in tax years beginning in 2018 are not subject to expiration. Federal NOLs that arose on or after January 1, 2018 can be carried forward indefinitely against future income, but can only be used to offset a maximum of 80% of the Company's federal taxable income in any year. The federal and state net operating loss carryforwards may be subject to significant limitations under Section 382 and Section 383 of the Internal Revenue Code and similar provisions under state law. Federal tax legislation enacted in December 2017, commonly known as the Tax Cuts and Jobs Act, contains provisions that limit the federal net operating loss carryforwards that may be used in any given year in the event of special occurrences, including significant ownership changes. A Section 382 “ownership change” generally occurs if one or more stockholders or groups of stockholders, who own at least 5% of the Company’s stock, increase their ownership by more than 50 percentage points over their lowest ownership percentage within a rolling three-year period. The Company may have previously experienced, and may in the future experience, one or more Section 382 “ownership changes,” including in connection with the Company’s initial public offering. If so, the Company may lose some or all of the tax benefits of its NOLs and tax credits. The extent of such limitations for prior years, if any, has not yet been formally determined. At December 31, 2021, the Company had $7,358,000 and $4,303,000 of federal and state research and development credit carryforwards, respectively, on a tax return basis. If not utilized, the federal credits will expire beginning in 2027. The California research and development credits can be carried forward indefinitely. As of December 31, 2021, the Company had $3,314,000 of unrecognized tax benefits. The Company does not have any tax positions for which it is reasonably possible that the total amount of gross unrecognized would increase or decrease within twelve months of the year ended December 31, 2021. If recognized, $0 would affect the effective tax rate. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense. There was no such expense recorded during the years ended December 31, 2021, 2020 and 2019. A reconciliation of the unrecognized tax benefits from January 1, 2019 to December 31, 2021 is as follows (in thousands) December 31, 2021 2020 2019Balance at the beginning of year $ 2,019 $ 1,436 $ 1,348Increases related to current years’ tax positions 704 342 88Increases related to prior years’ tax positions 591 241 —Balance at end of year $ 3,314 $ 2,019 $ 1,436 The Company currently has no federal or state tax examinations in progress nor has it had any federal or state tax examinations since its inception. As a result of the Company’s net operating loss carryforwards, all of its tax years are subject to federal and state tax examination.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

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+ Details

Summary of Significant Accounting Policies (Schedule of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies [Abstract]
Net loss	$ (49,811)	$ (47,365)	$ (52,415)
Weighted average common stock outstanding used to compute net loss per share, basic and diluted (in shares)	34,635,358	32,965,539	22,956,679
Net loss, basic and diluted (in USD per share)	$ (1.44)	$ (1.44)	$ (2.28)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events 2019 Equity Incentive Plan In January 2022, the number of shares of common stock authorized for issuance under the 2019 Plan was automatically increased by 1,399,235 shares, which was ratified by the Company's Board of Directors in February 2022. In January and February 2022, the Company approved the award of 21,357 RSU’s under the 2019 Plan. 2019 Employee Stock Purchase Plan In January 2022, the number of shares of common stock authorized for issuance under the 2019 ESPP was automatically increased by 349,808 shares, which was ratified by the Company's Board of Directors in February 2022.

Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 110,231	$ 69,466
Restricted cash	232	310
Total cash, cash equivalents and restricted cash	110,463	69,776	$ 39,491	$ 25,300
Letter of Credit [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 232	$ 310

Summary of Significant Accounting Policies - Advertising Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies [Abstract]
Advertising expense	$ 221	$ 194	$ 362

Income Taxes - Components of Income Before Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
United States	$ (49,811)	$ (47,365)	$ (52,415)
Total	$ (49,811)	$ (47,365)	$ (52,415)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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+ Details

Schedule II - Valuation and Qualifying Accounts - Schedule II (Details) - Allowance for doubtful accounts receivable: - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 13	$ 45	$ 22
Charged to expenses	6	(32)	23
Write offs	13
Balance at End of Year	$ 6	$ 13	$ 45

Summary of Significant Accounting Policies (Schedule of Potentially Dilutive Securities Not Included in Calculation of Earnings per Share) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	4,311,213	4,306,224	4,310,790
Common Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	3,780,939	4,237,828	4,310,790
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	530,274	68,396

Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 77,616	$ 63,069
Research and development credits	7,732	7,191
Capitalized start-up costs/Intangibles	4	8
Accruals and reserves	2,301	2,337
Stock-based compensation	4,392	1,859
Operating lease liability	1,751	935
Interest limitation	1,314	813
Total deferred tax assets	95,110	76,212
Less: Valuation allowance	(93,207)	(75,289)
Deferred tax liabilities:
Operating lease asset	(1,297)	(707)
Property and equipment	(606)	(216)
Total deferred tax liabilities	(1,903)	(923)
Net deferred tax assets

Balance Sheet Components (Available-for-Sale Investments in Unrealized Loss Position) (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 15,497
Unrealized Loss, Less than 12 months	(3)
Corporate Bonds/Notes [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	5,369
Unrealized Loss, Less than 12 months	(1)
U.S. Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	10,128
Unrealized Loss, Less than 12 months	$ (2)

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
Schedule II - Valuation and Qualifying Accounts	Dec. 31, 2021
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	All other schedules have been omitted because the information required to be set forth therein is not applicable or is shown in the financial statements or notes thereto. The table below presents Schedule II, Valuation and Qualifying Accounts, detailing the activity of the allowance for doubtful accounts receivable for the years ended December 31, 2021, 2020 and 2019 (in thousands): Description Balance at Beginning of Year Charged to expenses Write offs Balance at ‎End of YearAllowance for doubtful accounts receivable: Year ended December 31, 2021 $ 13 $ 6 $13 $ 6Year ended December 31, 2020 $ 45 $ (32) $— $ 13Year ended December 31, 2019 $ 22 $ 23 $— $ 45

Commitments and Contingencies - Purchase Obligation and Contingencies (Narrative) (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Commitments and Contingencies [Abstract]
Purchase obligation	$ 5,661,000
Contingent liabilities requiring accrual	$ 0	$ 0

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2021
Summary of Significant Accounting Policies [Abstract]
Basis of Preparation	Basis of Preparation The accompanying financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (“U.S. GAAP”).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts and disclosures reported in the financial statements. Management uses judgment when making estimates related to provisions for accounts receivable and excess and obsolete inventories, the valuation of deferred tax assets, the reserves for sales returns, stock-based compensation, and for periods prior to the Company's IPO, the valuation of common stock and redeemable convertible preferred stock warrants. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately differ from these estimates and assumptions. Due to the coronavirus (“COVID-19”) pandemic, there has been continued uncertainty and disruption in the global economy, supply chain, financial markets and increased labor shortages. While some of the uncertainties began to lift throughout the first half of 2021, new virus variants, and increased infection rates during the second half of 2021 continue to make the current COVID-related environment highly volatile and uncertain. These challenges continued to impact the number of TCAR procedures in 2021, with procedure volumes impacted by increased COVID-19 hospitalizations and hospital capacity constraints due to the COVID-19 and its variants. The Company is not aware of any specific event or circumstance that would require an update to its estimates or judgments or a revision of the carrying value of its assets or liabilities as of December 31, 2021. The Company has also considered information available to it as of the date of issuance of these financial statements and is not aware of any specific events or circumstances that would require an update to its estimates or judgments, or a revision to the carrying value of its assets or liabilities. These estimates may change as new events occur and additional information becomes available. Actual results could differ materially from these estimates.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company has evaluated the estimated fair value of its financial instruments as of December 31, 2021 and 2020. The carrying amounts of certain of the Company’s financial instruments, which include cash equivalents, short-term investments, restricted cash, accounts receivable, accounts payable and accrued liabilities approximate their respective fair values because of the short-term nature of these instruments. Management believes that its short-term and long-term debt bears interest at the prevailing market rates for instruments with similar characteristics (Level 2 within the fair value hierarchy); accordingly, the carrying value of this instrument approximates its fair value. Prior to the Company's IPO, fair value accounting was applied to the redeemable convertible preferred stock warrant liability.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with an original maturity of three months or less at the time of purchase to be cash equivalents. Cash equivalents are considered available-for-sale marketable securities and are recorded at fair value, based on quoted market prices. As of December 31, 2021, the Company’s cash equivalents are comprised of investments in money market funds. As of December 31, 2020, the Company’s cash equivalents comprised investments in money market funds and commercial paper. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the balance sheets that sum to the total of the same amounts shown in the statements of cash flows (in thousands): December 31, 2021 2020Cash and cash equivalents $ 110,231 $ 69,466Restricted cash 232 310Total cash, cash equivalents and restricted cash $ 110,463 $ 69,776 Restricted cash as of December 31, 2021 and 2020 consists of a letter of credit of $232,000 and $310,000, respectively, representing collateral for the Company’s facility lease in California.
Investments	Investments Short-term investments consist of debt securities classified as available-for-sale and have original maturities greater than 90 days, but less than one year as of the balance sheet date. Long-term investments have maturities greater than one year as of the balance sheet date. All investments are recorded at fair value based on the fair value hierarchy. Money market funds are classified within Level 1 of the fair value hierarchy, and commercial paper, corporate bonds/notes, United States Government securities, and asset-backed securities are classified within Level 2 of the fair value hierarchy. Unrealized gains and losses, deemed temporary in nature, are reported as a separate component of accumulated other comprehensive income (loss). The cost of available-for-sale investments sold is based on the specific-identification method. Realized gains and losses are included in earnings and are derived for specific-identification method for determining the costs of investments sold and were insignificant for the year ended December 31, 2021, 2020 and 2019. Amortization of premiums and accretion of discounts are reported as a component of interest income. A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the investment. The Company evaluates the securities in an unrealized loss position for expected credit losses by considering factors such as historical experience, market data, issuer-specific factors, current economic conditions and credit ratings.
Concentration of Credit Risk, and Other Risks and Uncertainties	Concentration of Credit Risk, and Other Risks and Uncertainties The Company is subject to risks related to public health crises such as the global pandemic associated with COVID-19. The COVID-19 outbreak has negatively impacted, and may continue to negatively impact the Company’s operations, its revenue and overall financial condition by significantly decreasing the number of TCAR procedures performed. The number of TCAR procedures performed, similar to other surgical procedures, has significantly decreased as health care organizations globally prioritized the treatment of patients with COVID-19. In the past governmental authorities have recommended, and in certain cases required, that elective, specialty and other procedures and appointments, be suspended or canceled to focus limited resources and personnel and hospital capacity toward the treatment of COVID-19 and to avoid exposing patients to COVID-19. These measures and challenges will likely continue for the duration of the pandemic, which is uncertain, and will continue to negatively impact the Company’s revenue while the pandemic continues. New virus variants, and increased infection rates continue to make the current COVID-related environment highly volatile and uncertain. Financial instruments that potentially subject the Company to credit risk consist of cash and cash equivalents, investments and accounts receivable to the extent of the amounts recorded on the balance sheet. Cash, cash equivalents, and investments are deposited in financial institutions which, at times, may be in excess of federally insured limits. Cash equivalents are invested in highly rated money market funds. The Company invests in a variety of financial instruments, such as, but not limited to, commercial paper, corporate bonds/notes, United States Government securities, asset-backed securities and, by policy, limits the amount of credit exposure with any one financial institution or commercial issuer. The Company has not experienced any material losses on its deposits of cash and cash equivalents or investments during the years ended December 31, 2021 and 2020. The Company’s accounts receivable are due from a variety of health care organizations in the United States. At December 31, 2021 and 2020, no customer represented 10% or more of the Company’s accounts receivable. For the years ended December 31, 2021, 2020 and 2019, there were no customers that represented 10% or more of revenue. The Company provides for uncollectible amounts when specific credit problems are identified. In doing so, the Company analyzes historical bad debt trends, customer credit worthiness, current economic trends and changes in customer payment patterns when evaluating the adequacy of the allowance for expected credit losses on customer accounts. The Company manufactures certain of its commercial products in-house. Certain of the Company’s product components and sub-assemblies continue to be manufactured by sole suppliers, the most significant of which is the ENROUTE Transcarotid Stent System, manufactured by Cordis Corporation. Disruption in component or sub-assembly supply from these manufacturers or from in-house production would have a negative impact on the Company’s financial position and results of operations. The Company is subject to certain risks, including that its devices may not be approved or cleared for marketing by governmental authorities or be successfully marketed. There can be no assurance that the Company’s products will achieve widespread adoption in the marketplace, nor can there be any assurance that existing devices or any future devices can be developed or manufactured at an acceptable cost and with appropriate performance characteristics. The Company is also subject to risks common to companies in the medical device industry, including, but not limited to, new technological innovations, dependence upon government and third-party payers to provide adequate coverage and reimbursement, dependence on key personnel and suppliers, protection of proprietary technology, product liability claims, and compliance with government regulations. Existing or future devices developed by the Company may require approvals or clearances from the FDA or international regulatory agencies. In addition, in order to continue the Company’s operations, compliance with various federal and state laws is required. If the Company were denied or delayed in receiving such approvals or clearances, it may be necessary to adjust operations to align with the Company’s currently approved portfolio. If clearance for the products in the current portfolio were withdrawn by the FDA, this would have a material adverse impact on the Company.
Voluntary Recall	Voluntary Recall In January and February 2021, the Company announced the voluntary recall of certain lots of its ENROUTE Transcarotid Stent System, manufactured by one of its third-party suppliers, Cordis. The decision to recall these lots was based on complaints received about tips detaching from the stent delivery system as well as internal testing that the Company conducted. The Company believes the root cause of the detachment was a single operator at Cordis, who, over a specific timeframe, produced lots in which a small number of units were not reliably manufactured to specification. As a result of the voluntary recall the Company reflected a current asset of $4,160,000 on its balance sheet as of December 31, 2020, relating to the replacement lots and other direct costs to be received from Cordis. This amount included $2,227,000 of recalled ENROUTE stent delivery systems held in the Company's inventory as of December 31, 2020, $1,696,000 of ENROUTE stent delivery systems in the process of being returned from its customers and other direct costs of $237,000. In addition, the Company established an accrual of $1,696,000 relating to its obligation to provide replacement ENROUTE stent delivery systems to its customers as of December 31, 2020. As of December 31, 2021, the Company has a current asset of $335,000 on its balance sheet relating to other direct costs that remain to be reimbursed from Cordis. In addition, as of December 31, 2021, the Company has a remaining accrual of $11,000 relating to its obligation to provide replacement ENROUTE stent delivery systems to its customers.
Accounts Receivable	Accounts Receivable Trade accounts receivable are recorded at the invoiced amount and do not bear interest. The Company estimates allowances for expected credit losses. Specifically, the Company makes estimates on the collectability of customer accounts based primarily on analysis of historical trends and experience and changes in customers’ financial condition. The Company uses its judgment, based on the best available facts and circumstances, and records an allowance against amounts due to reduce the receivable to the amount that is expected to be collected. These specific allowances are reevaluated and adjusted as additional information is received that impacts the amount reserved. During the years ended December 31, 2021, 2020 and 2019, the Company did not experience any material credit-related losses.
Inventories	Inventories Inventories are valued at the lower of cost to purchase or manufacture the inventory or net realizable value. Cost is determined using the first-in, first-out method for all inventories. Net realizable value is determined as the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. The Company regularly reviews inventory quantities in consideration of actual loss experiences, projected future demand, and remaining shelf life prior to sale to record a provision for excess and obsolete inventory when appropriate. The Company’s policy is to write down inventory that has become obsolete, inventory that has a cost basis in excess of its expected lower of cost or net realizable value, and inventory in excess of expected requirements. The estimate of excess quantities is judgmental and primarily dependent on the Company’s estimates of future demand for a particular product. If the estimate of future demand is too high, the Company may have to increase the reserve for excess inventory for that product and record a charge to the cost of goods sold.
Other Current Assets	Other Current Assets The prepaid expenses and other current assets balance at December 31, 2020 included $4,160,000 associated with the Company's voluntary recall. The amount relates to the replacement lots and other direct costs to be received from Cordis. As of December 31, 2021, the Company has a current asset of $335,000 on its balance sheet relating to other direct costs that remain to be reimbursed from Cordis.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost less accumulated depreciation or amortization. Repairs and maintenance costs are expensed as incurred. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the assets, typically three years to five years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or estimated useful economic life of the asset. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in operations in the period realized.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. If indicators of impairment exist, an impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the assets and their eventual disposition are less than their carrying amount. Impairment, if any, is measured as the amount by which the carrying amount of the long-lived assets exceeds their fair value. The Company did not record any impairment of long-lived assets during the years ended December 31, 2021, 2020 and 2019.
Leases	Leases The Company accounts for its leasing arrangements in accordance with Accounting Standards Codification (“ASC”) 842, “Leases.” The Company considers if an arrangement is a lease at inception if it obtains the right to control the use of an identified asset under a leasing arrangement with an initial term greater than twelve months. The Company determines whether a contract conveys the right to control the use of an identified asset for a period of time if the contract contains both the right to obtain substantially all of the economic benefits from the use of the identified asset and the right to direct the use of the identified asset. The Company also evaluates the nature of each lease to determine whether it is an operating or financing lease and recognizes the right-of-use asset and lease liabilities based on the present value of future minimum lease payments over the expected lease term. The Company’s leases do not generally contain an implicit interest rate and therefore the Company uses the incremental borrowing rate it would expect to pay to borrow on a similar collateralized basis over a similar term in order to determine the present value of its lease payments. The Company considers renewal options in the determination of the lease term if the option to renew is reasonably certain. Variable lease costs represent payments that are dependent on usage, a rate or index. Variable lease costs, which consists primarily of taxes, insurance and common area maintenance costs, are expensed as incurred. The Company elected to account for contracts that contain lease and non-lease components as a single component, consistent with its historical practice. The Company does not have any finance leases.
Redeemable Convertible Preferred Stock Warrant Liability	Redeemable Convertible Preferred Stock Warrant Liability Prior to its IPO, the Company accounted for its warrants for shares of redeemable convertible preferred stock as a liability based upon the characteristics and provisions of each instrument. Redeemable convertible preferred stock warrants classified as a liability were initially recorded at their fair value on the date of issuance and are subject to remeasurement at each subsequent balance sheet date. Any change in fair value as a result of a remeasurement was recognized as a component of other income (expense), net in the statements of operations and comprehensive loss. The Company recorded adjustments to the estimated fair value of the redeemable convertible preferred stock warrants until they were exercised. Upon their exercise, the final fair value of the warrant liability was reclassified to stockholders’ equity. Subsequent to its IPO, the Company no longer recorded any related periodic fair value adjustments.
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock Prior to its IPO, the Company recorded its redeemable convertible preferred stock at fair value on the dates of issuance, net of issuance costs, and classified the redeemable convertible preferred stock outside of stockholders’ equity on the balance sheet as events triggering the liquidation preferences were not solely within the Company’s control. Upon the closing of the Company's IPO, all shares of convertible preferred stock then outstanding converted into an aggregate of 23,178,555 shares of common stock resulting in the reclassification of $144,140,000 from outside of stockholders’ equity to additional paid-in capital.
Revenue Recognition and Cost of Goods Sold	Revenue Recognition The Company recognizes revenue in accordance with ASC Topic 606, "Revenue from Contracts with Customers." Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the Company performs the following five steps: (i)identify the contract(s) with a customer; (ii)identify the performance obligations in the contract; (iii)determine the transaction price; (iv)allocate the transaction price to the performance obligations in the contract; and (v)recognize revenue when (or as) the entity satisfies a performance obligation. As of December 31, 2021 and 2020, the Company recorded $87,000 and $71,000, respectively, of unbilled receivables, which are included in accounts receivable, net on the balance sheet, as the Company has an unconditional right to payment as of the end of the applicable period. The Company’s revenue is generated from the sale of its products to hospitals and medical centers in the United States through direct sales representatives. Revenue is recognized when obligations under the terms of a contract with customers are satisfied, which occurs with the transfer of control of the Company’s products to its customers, either upon shipment of the product or delivery of the product to the customer under the Company’s standard terms and conditions. The Company’s products are readily available for usage as soon as the customer possesses it. Upon receipt, the customer controls the economic benefits of the product, has significant risks and rewards, and the legal title. The Company has present right to payment; therefore, the transfer of control is deemed to happen at a point in time. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring the goods. For sales where the Company’s sales representative hand delivers product directly to the hospital or medical center from the sales representative’s trunk stock inventory, the Company recognizes revenue upon delivery, which represents the point in time when control transfers to the customer. Upon delivery there are legally-enforceable rights and obligations between the parties which can be identified, commercial substance exists and collectability is probable. For sales which are sent directly from the Company to hospitals and medical centers, the transfer of control occurs at the time of shipment or delivery of the product. There are no further performance obligations by the Company or the sales representative to the customer after delivery under either method of sale. As allowed under the practical expedient, the Company does not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii) contracts for which it recognizes revenue at the amount to which it has the right to invoice for services performed. The Company is entitled to the total consideration for the products ordered by customers as product pricing is fixed according to the terms of customer contracts and payment terms are short. Payment terms fall within the one-year guidance for the practical expedient which allows the Company to forgo adjustment of the promised amount of consideration for the effects of a significant financing component. The Company excludes taxes assessed by governmental authorities on revenue-producing transactions from the measurement of the transaction price. Costs associated with product sales include commissions and royalties. The Company applies the practical expedient and recognizes commissions and royalties as expense when incurred because the expense is incurred at a point in time and the amortization period is less than one year. Commissions are recorded as selling expense and royalties are recorded as cost of goods sold in the statements of operations and comprehensive loss. The Company accepts product returns at its discretion or if the product is defective as manufactured. The Company establishes estimated provisions for returns based on historical experience and considers other factors that it believes could significantly impact its expected returns, which provisions are classified within accrued liabilities on our balance sheet. The Company elected to expense shipping and handling costs as incurred and includes them in the cost of goods sold. In those cases where the Company bills shipping and handling costs to customers, it will classify the amounts billed as a component of revenue. Cost of Goods Sold The Company manufactures certain of its portfolio of TCAR products at its California facility and purchases other products from third party manufacturers. Cost of goods sold consists primarily of costs related to materials, components and sub-assemblies, manufacturing overhead costs, direct labor, reserves for excess, obsolete and non-sellable inventories as well as distribution-related expenses. A significant portion of the Company’s cost of goods sold currently consists of manufacturing overhead costs. These overhead costs include the cost of quality assurance, material procurement, inventory control, facilities, equipment and operations supervision and management. Cost of goods sold also includes depreciation expense for production equipment and certain direct costs such as shipping costs and royalties. In May 2021, the Company entered into a lease for an additional facility in Minnesota and expects to begin commercial production in the second half of 2022. During this time the Company experienced additional overhead related to manufacturing start-up and expansion of its manufacturing capacity, which were recorded as a period expense.
Research and Development and Clinical Trials	Research and Development The Company expenses research and development costs as incurred. Research and development expenses consist primarily of engineering, product development, clinical studies to develop and support the Company’s products, regulatory expenses, medical affairs and other costs associated with products and technologies that are in development. Research and development expenses include employee compensation, including stock-based compensation, supplies, consulting, prototyping, testing, materials, travel expenses, depreciation and an allocation of facility overhead expenses. Additionally, research and development expenses include costs associated with our clinical studies including clinical trial design, clinical site reimbursement, data management, travel expenses and the cost of products used for clinical trials and internal and external costs associated with the Company’s regulatory compliance and quality assurance functions, including the costs of outside consultants and contractors that assist in the process of submitting and maintaining regulatory filings, and overhead costs. Clinical Trials The Company accrues and expenses costs for its clinical trial activities performed by third parties, including clinical research organizations and other service providers, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company determines these accruals through discussion with internal personnel and outside service providers as to progress or stage of completion of trials or services pursuant to contracts with clinical research organizations and other service providers and the agreed-upon fee to be paid for such services.
Advertising Costs	Advertising Costs The Company expenses advertising costs as incurred. Advertising costs include design and production costs, including website development, physician and patient testimonial videos, written media campaigns, and other items. Advertising costs of $221,000, $194,000 and $362,000 were expensed during the years ended December 31, 2021, 2020 and 2019, respectively.
Foreign Currency	Foreign Currency The Company records net gains and losses resulting from foreign exchange transactions as a component of foreign currency exchange gains or losses in other income (expense), net. The Company had no material foreign currency exchange gains or losses during the years ended December 31, 2021, 2020 and 2019.
Stock-Based Compensation	Stock–Based Compensation The Company accounts for stock-based compensation in accordance with Financial Accounting Standards Board (“FASB”) ASC 718, “Compensation-Stock Compensation.” ASC 718 requires the recognition of compensation expense, using a fair-value based method, for costs related to all share-based payments including stock options, restricted stock units and shares issued under its employee stock purchase plan. ASC 718 requires companies to estimate the fair value of all share-based payment option awards on the date of grant using an option pricing model. The fair value of stock options is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period), on a straight-line basis. For performance-based stock options, the Company will assess the probability of performance conditions being achieved in each reporting period. The amount of stock-based compensation expense recognized in any one period related to performance-based stock options can vary based on the achievement or anticipated achievement of the performance conditions. The Company accounts for option forfeitures as they occur. The Company accounts for stock-based compensation for restricted stock units at their fair value, based on the closing market price of the Company's common stock on the date of grant. These costs are recognized on a straight-line basis over the requisite service period, which is usually the vesting period. The Company accounts for stock-based compensation for its employee stock purchase plan based on the estimated fair value of the options on the date of grant. The Company estimates the grant date fair value using an option pricing model for each purchase period. These costs are recognized on a straight-line basis over the offering period.
Income Taxes	Income Taxes The Company accounts for income taxes under the liability method, whereby deferred tax assets and liabilities are determined based on the difference between the financial statements and tax bases of assets and liabilities using the enacted tax rates in effect for the year in which the differences are expected to affect taxable income. A valuation allowance is established when necessary to reduce deferred tax assets to the amounts expected to be realized. As the Company has historically incurred operating losses, it has established a full valuation allowance against its net deferred tax assets, and there is no provision for income taxes. The Company also follows the provisions of ASC 740-10, “Accounting for Uncertainty in Income Taxes.” ASC 740-10 prescribes a comprehensive model for the recognition, measurement, presentation and disclosure in financial statements of any uncertain tax positions that have been taken or expected to be taken on a tax return. No liability related to uncertain tax positions is recorded on the financial statements. It is the Company’s policy to include penalties and interest expense related to income taxes as part of the provision for income taxes.
Comprehensive Loss	Comprehensive Loss Comprehensive loss consists of net loss and changes in unrealized gains and losses on investments classified as available-for-sale. For the years ended December 31, 2021, 2020 and 2019, the Company’s unrealized gains and losses on available-for-sale investments represent the only component of other comprehensive loss that are excluded from the reported net loss and that are presented in the statements of operations and comprehensive income. Accumulated other comprehensive loss is presented in the accompanying balance sheets as a component of stockholders' equity.
Net Loss per Share	Net Loss per Share Basic net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration for potential dilutive common shares. Diluted net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, redeemable convertible preferred stock and warrants, common stock options, and restricted stock units are considered to be potentially dilutive securities. Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share as the inclusion of all potential dilutive common shares would have been anti-dilutive. The Company allocates no loss to participating securities because they have no contractual obligation to share in the losses of the Company. The shares of the Company’s redeemable convertible preferred stock participate in any dividends declared by the Company and are therefore considered to be participating securities. Net loss per share was determined as follows (in thousands, except share and per share data): Year Ended December 31, 2021 2020 2019Net loss $ (49,811) $ (47,365) $ (52,415)Weighted average common stock outstanding used to compute net loss per share, basic and diluted 34,635,358 32,965,539 22,956,679Net loss per share, basic and diluted $ (1.44) $ (1.44) $ (2.28) The following potentially dilutive securities outstanding have been excluded from the computation of diluted weighted average shares outstanding because such securities have an antidilutive impact due to the Company’s net loss: December 31, 2021 2020 2019Common stock options 3,780,939 4,237,828 4,310,790Restricted stock units 530,274 68,396 —Total 4,311,213 4,306,224 4,310,790
Segment and Geographical Information	Segment and Geographical Information The Company operates and manages its business as one reportable and operating segment. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. Primarily all of the Company’s long-lived assets are based in the United States. Long-lived assets are comprised of property and equipment. All of the Company’s revenue was in the United States for the years ended December 31, 2021, 2020 and 2019, based on the shipping location of the external customer.

Balance Sheet Components (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Components [Abstract]
Depreciation and amortization	$ 1,032	$ 789	$ 712
Cash Equivalents, at Carrying Value	$ 21,062

Redeemable Convertible Preferred Stock	12 Months Ended
Redeemable Convertible Preferred Stock	Dec. 31, 2021
Redeemable Convertible Preferred Stock [Abstract]
Redeemable Convertible Preferred Stock	8. Redeemable Convertible Preferred Stock Upon the closing of the Company's IPO, all shares of redeemable convertible preferred stock then outstanding converted into shares of common stock. As of December 31, 2021 and 2020, the Company does not have any redeemable convertible preferred stock issued or outstanding. Redeemable Convertible Preferred Stock Warrants Upon the closing of the Company's IPO, all of the outstanding redeemable convertible preferred stock warrants were exercised, or net exercised based on the IPO price of $20.00 per share, into 1,945,365 shares of common stock. As of December 31, 2021 and 2020, the Company does not have any redeemable convertible preferred stock warrants outstanding.

Summary of Significant Accounting Policies - Segment and Geographical Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2021 segment
Summary of Significant Accounting Policies [Abstract]
Number of reportable segments	1
Number of operating segments	1

Stock Option Plans (Tables)	12 Months Ended
Stock Option Plans (Tables)	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Shares Available for Issuance	Number of SharesBalances, December 31, 2018 57,889Authorized 2,317,000Granted (848,023)Canceled 27,824Balances, December 31, 2019 1,554,690Authorized 1,250,210Granted/Awarded (1,079,883)Cancelled 65,670Balances, December 31, 2020 1,790,687Authorized 1,369,985Granted/Awarded (847,080)Cancelled 163,620Balances, December 31, 2021 2,477,212
Stock Option Activity	Options Outstanding Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in Years) Aggregate Intrinsic Value (in thousands)Balances, December 31, 2018 4,364,377 $3.79 7.36 $33,132 Options granted 848,023 $22.77 Options exercised (873,786) $1.77 Options cancelled (27,824) $8.71 Balances, December 31, 2019 4,310,790 $7.91 7.27 $140,234 Options granted 1,010,843 $40.67 Options exercised (1,018,779) $3.42 Options cancelled (65,026) $23.32 Balances, December 31, 2020 4,237,828 $16.56 7.38 $197,407 Options granted 323,057 $ 53.94 Options exercised (643,507) $ 7.49 Options cancelled (136,439) $ 40.30 Balances, December 31, 2021 3,780,939 $ 20.45 6.71 $ 91,900Vested and exercisable at December 31, 2021 2,732,674 $ 13.64 6.13 $ 81,395Vested and expected to vest at December 31, 2021 3,780,939 $ 20.45 6.71 $ 91,900
Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block]	Options Outstanding Options VestedExercise Price Options Outstanding Weighted Average Remaining Contractual Term (in Years) Weighted Average Exercise Price Number Exercisable Weighted Average Exercise Price$1.35 - $3.16 868,256 4.58 $ 2.05 868,256 $ 2.05$4.73 - $7.10 577,759 6.17 $ 5.74 542,305 $ 5.71$8.27 - $12.41 490,391 6.06 $ 11.74 470,037 $ 11.83$20.00 - $30.00 616,871 7.26 $ 20.00 400,815 $ 20.00$30.93 - $46.40 682,913 8.12 $ 33.60 308,065 $ 34.34$47.20 - $70.80 544,749 8.86 $ 57.22 143,196 $ 57.48 3,780,939 6.71 $ 20.45 2,732,674 $ 13.64
Summary of RSU Activity	Number of Restricted Stock Units Weighted Average Grant Date Fair ValueBalances, December 31, 2019 — $ —Restricted stock granted 69,040 $ 46.14Restricted stock vested — $ —Restricted stock forfeited (644) $ 44.62Balances, December 31, 2020 68,396 $ 46.16Restricted stock granted 524,023 $ 53.64Restricted stock vested (34,964) $ 49.95Restricted stock forfeited (27,181) $ 51.99Balances, December 31, 2021 530,274 $ 53.01Expected to vest at December 31, 2021 530,274 $ 53.01
Stock-Based Compensation Expense Relating to Stock Options to Employees and Nonemployees	Year Ended December 31, 2021 2020 2019 Cost of goods sold$ 635 $ 339 $ 179Research and development expenses 2,909 1,110 426Selling, general and administrative expenses 11,068 5,777 2,372 $ 14,612 $ 7,226 $ 2,977
Common Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Fair Value Assumptions	Year Ended December 31, 2021 2020 2019Expected term (in years) 5.25 - 6.25 5.00 - 6.25 5.00 - 6.25Expected volatility 45.0% - 50.4% 43.0% - 50.3% 42.4% - 42.9%Risk-free interest rate 0.41% - 1.08% 0.32% - 1.41% 1.47% - 2.54%Dividend yield —% —% —%
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Fair Value Assumptions	Year Ended December 31, 2021 2020 2019Expected term (in years) 0.50 0.50 0.50 - 0.63Expected volatility 46.9% - 51.6% 44.4% - 76.4% 44.4% - 47.8%Risk-free interest rate 0.03% - 0.10% 0.10% - 1.58% 1.58% - 2.45%Dividend yield —% —% —%

Stockholders' Equity (Deficit) - Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	7,180,248	6,660,892
Exercise of options under stock plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	3,780,939	4,237,828
Issuance of options and restricted stock units under stock plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	2,477,212	1,790,687
ESPP [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	922,097	632,377

Summary of Significant Accounting Policies - Voluntary Recall (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Inventory [Line Items]
Inventories	$ 17,851,000	$ 9,989,000
Contingent liabilities requiring accrual	0	0
ENROUTE [Member]
Inventory [Line Items]
Inventories		2,227,000
Inventory Recall Expense	335,000
Contingent liabilities requiring accrual	11,000
ENROUTE, Held By Customer [Member]
Inventory [Line Items]
Inventory Recall Expense		237,000
Contingent liabilities requiring accrual		1,696,000
Voluntary Recall
Inventory [Line Items]
Other Assets, Current		$ 4,160,000
Contingent liabilities requiring accrual	$ 1,696,000

Stock Option Plans (Activity Under Compensation Plan) (Details) - 2019 Equity Incentive Plan [Member] - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Shares Available for Grant
Beginning balance (in shares)	1,790,687	1,554,690	57,889
Authorized (in shares)	1,369,985	1,250,210	2,317,000
Granted/Awarded (in shares)	(847,080)	(1,079,883)	(848,023)
Canceled (in shares)	163,620	65,670	27,824
Ending balance (in shares)	2,477,212	1,790,687	1,554,690

Fair Value Measurements	12 Months Ended
Fair Value Measurements	Dec. 31, 2021
Fair Value Measurements [Abstract]
Fair Value Measurements	4. Fair Value Measurements The Company measures certain financial assets and liabilities at fair value on a recurring basis, including cash equivalents, investments, and the Company's previously outstanding preferred stock warrants. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. A three-tier fair value hierarchy is established as a basis for considering such assumptions and for inputs used in the valuation methodologies in measuring fair value: •Level 1 – quoted prices in active markets are identical assets and liabilities; •Level 2 – observable inputs other than quotes prizes in active markets for identical assets and liabilities; •Level 3 – unobservable inputs. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. The Company’s cash equivalents are classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. The corporate bonds/notes, commercial paper, asset-backed securities and U.S. government securities are classified as Level 2 as they are valued based upon quoted market prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. The following table sets forth by level within the fair value hierarchy the Company’s assets and liabilities that are reported at fair value as of December 31, 2021 and 2020 using the inputs defined above (in thousands): December 31, 2021 Level 1 Level 2 Level 3 TotalAssets: Money market funds$ 21,062 $— $— $ 21,062 $ 21,062 $ — $— $ 21,062 December 31, 2020 Level 1 Level 2 Level 3 TotalAssets: Money market funds$ 60,295 $— $— $ 60,295Commercial paper — 39,577 — 39,577Corporate bonds/notes — 7,969 — 7,969U.S. government securities — 38,470 — 38,470 $ 60,295 $ 86,016 $— $ 146,311 There were no transfers between fair value hierarchy levels during the years ended December 31, 2021 and 2020.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Increase (decrease) in deferred tax asset valuation allowance	$ 17,918,000	$ 22,163,000
Unrecognized tax benefits	3,314,000	2,019,000	$ 1,436,000	$ 1,348,000
Unrecognized tax benefits that would impact effective tax rate	0
Unrecognized tax benefits, income tax penalties and interest expense	0	$ 0	$ 0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	301,306,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	254,476,000
Research Tax Credit Carryforward \| Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	7,358,000
Research Tax Credit Carryforward \| State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 4,303,000

Formation and Business of the Company (Details) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	Mar. 19, 2019	May 31, 2020 USD ($) $ / shares shares	Aug. 31, 2019 $ / shares shares	Apr. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2021 USD ($)
Subsequent Event [Line Items]
Accumulated deficit					$ (238,891)		$ (288,702)
Cash and cash equivalents					69,466		$ 110,231
Reverse stock split	2.7
Issued and sold common stock (in shares) \| shares		6,808,154		6,000,000
Net proceeds		$ 70,543		$ 109,119
Stock issued, price per share (in USD per share) \| $ / shares		$ 39.00	$ 39.50	$ 20.00
Payments of deferred offering costs		$ 707		$ 2,481	$ 4,457	$ 10,961
Payment of stock issuance underwriting discounts and commissions		$ 3,750		$ 8,400
Public Stock Offering Shares From Company [Member]
Subsequent Event [Line Items]
Issued and sold common stock (in shares) \| shares		1,923,076
Public Stock Offering Shares From Existing Shareholders [Member]
Subsequent Event [Line Items]
Issued and sold common stock (in shares) \| shares		4,885,078	4,200,000
Over Allotment [Member]
Subsequent Event [Line Items]
Issued and sold common stock (in shares) \| shares		1,021,223	630,000

Balance Sheet Components (Fair Value of Available-For-Sale Investments) (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 146,272
Gross Unrealized Gains	42
Gross Unrealized Losses	(3)
Estimated Fair Value	146,311
Money Market Funds [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	60,295
Estimated Fair Value	60,295
Commercial Paper [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	39,577
Estimated Fair Value	39,577
Corporate Bonds/Notes [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,970
Gross Unrealized Losses	(1)
Estimated Fair Value	7,969
U.S. Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	38,430
Gross Unrealized Gains	42
Gross Unrealized Losses	(2)
Estimated Fair Value	38,470
Cash Equivalents [Member]
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	68,295
Short-Term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 78,016

Balance Sheet Components (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Components [Abstract]
Accrued payroll and related expenses	$ 13,898	$ 9,573
Provision for sales returns	359	820
Accrued professional services	2,039	2,520
Recall replacement obligation	11	1,696
Operating lease liability	1,294	850
Accrued royalty expense	687	518
Deferred revenue	157	206
Accrued travel expenses	590	237
Accrued clinical expenses	99	113
Accrued other expenses	668	424
Total	$ 19,802	$ 16,957

Commitments and Contingencies (Balance Sheet Information) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Commitments and Contingencies [Abstract]
Operating lease right-of-use asset in other non-current assets	$ 5,219	$ 2,798
Operating lease liability in accrued liabilities	1,294	850
Operating lease liability in other liabilities	5,747	2,850
Total operating lease liabilities	$ 7,041	$ 3,700

Stock Option Plans (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
Stock Option Plans (Narrative) (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of options exercised		$ 29,355,000	$ 47,861,000	$ 24,867,000
Weighted average grant date fair value (in USD per share)		$ 23.83	$ 18.22	$ 10.17
Fair value of options vested		$ 9,076,000	$ 5,138,000	$ 2,221,000
Common stock reserved for future issuance (in shares)		7,180,248	6,660,892
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grant Date Fair Value		$ 28,110,000	$ 3,186,000
ISO and NSO [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting term		4 years
ISO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise threshold as a percentage of fair value of shares		100.00%
Percent of purchase of price of common stock		10.00%
NSO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise threshold as a percentage of fair value of shares		85.00%
Percent of purchase of price of common stock		110.00%
2019 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expensed not yet recognized, period for recognition		4 months 17 days
Unrecognized compensation costs related to the ESPP		$ 365,000
Common Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expensed not yet recognized		$ 16,737,000
Compensation expensed not yet recognized, period for recognition		2 years 4 months 13 days
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expensed not yet recognized, period for recognition		3 years 3 months 25 days
Unrecognized compensation costs of unvested RSUs		$ 24,183,000
2019 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance (in shares)					2,317,000
Number of additional shares allowable under the plan (in shares)		3,000,000
Percent of outstanding shares of common stock		4.00%
Common stock reserved for future issuance (in shares)	434,000	5,016,420
Additional Common Stock Capital Shares Reserved For Future Issuance	1,200,000
Percent Of Outstanding Shares	1.00%
2019 Equity Incentive Plan [Member] \| Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting term		4 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value		$ 1,893,000	$ 0
ESPP, 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)		1,089,048
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued		166,951
Shares available for future issuance (in shares)		922,097
Fair Market Value Of Common Stock		85.00%

Commitments and Contingencies (Operating Lease Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Commitments and Contingencies [Abstract]
2022	$ 620
2023	1,967
2024	1,764
2025	882
2026	904
Thereafter	2,769
Total lease payments	8,906
Less: interest	(1,865)
Total lease liabilities	$ 7,041	$ 3,700

Formation and Business of the Company	12 Months Ended
Formation and Business of the Company	Dec. 31, 2021
Balance Sheet Components [Abstract]
Formation and Business of the Company	1. Formation and Business of the Company The Company Silk Road Medical, Inc. (the “Company”) was incorporated in the state of Delaware on March 21, 2007. The Company has developed a technologically advanced, minimally-invasive solution for patients with carotid artery disease who are at risk for stroke. The Company’s portfolio of TCAR products enable a new procedure, referred to as transcarotid artery revascularization, or TCAR, that combines the benefits of endovascular techniques and surgical principles. The Company manufactures and sells in the United States its portfolio of TCAR products which are designed to provide direct access to the carotid artery, effective reduction in stroke risk throughout the procedure, and long-term restraint of carotid plaque. The Company commercialized its products in the United States in late 2015. Liquidity In the course of its activities, the Company has incurred losses and negative cash flows from operations since its inception. As of December 31, 2021, the Company had an accumulated deficit of $288,702,000. The Company expects to incur losses for the foreseeable future. The Company believes that its cash and cash equivalents of $110,231,000 at December 31, 2021, as well as its expected revenues will provide sufficient funds to allow the Company to fund its planned current operations for the next twelve months from the issuance of these financial statements. Reverse Stock Split On March 13, 2019, the Company’s Board of Directors approved an amendment to the Company’s amended and restated certificate of incorporation to effect a 1-for-2.7 reverse stock split of the Company’s common stock and redeemable convertible preferred stock to be consummated prior to the effectiveness of the Company’s planned initial public offering (“IPO”). The reverse stock split was effected on March 27, 2019. The par values of the common stock and redeemable convertible preferred stock were not adjusted as a result of the reverse stock split. All the common stock, redeemable convertible preferred stock, stock options and warrants, and related per share amounts in the financial statements have been retroactively adjusted for all periods presented to give effect to the reverse stock split. Public Offerings In April 2019, the Company issued and sold 6,000,000 shares of its common stock in its IPO at a public offering price of $20.00 per share, for net proceeds of approximately $109,119,000 after deducting underwriting discounts and commissions of approximately $8,400,000 and expenses of approximately $2,481,000. Upon the closing of the IPO, all shares of redeemable convertible preferred stock then outstanding converted into shares of common stock and the Company's outstanding warrants to purchase shares of common and redeemable convertible preferred stock were exercised, or automatically net exercised absent a prior election. The exercises resulted in the reclassification of the fair value of the related redeemable convertible preferred stock warrant liability to additional paid-in capital. In August 2019, the Company completed a secondary public offering of 4,200,000 shares of its common stock sold by certain selling stockholders, and the exercise in full of the underwriters' option to purchase 630,000 additional shares of its common stock from certain selling stockholders, at a public offering price of $39.50 per share. The Company did not receive any of the proceeds from the sale of the shares of its common stock from the selling stockholders. In May 2020, the Company completed an underwritten public offering of 6,808,154 shares of its common stock, of which 1,923,076 shares were offered for sale by the Company and the remaining 4,885,078 shares were offered for sale by certain selling stockholders, at a public offering price of $39.00 per share. The Company received cash proceeds of approximately $70,543,000 after deducting underwriting discounts and commissions of approximately $3,750,000 and expenses of approximately $707,000. Also, in May 2020, the underwriters fully exercised their option to purchase 1,021,223 additional shares of common stock from the selling stockholders. The Company did not receive any of the proceeds from the sale of the shares of its common stock by the selling stockholders.

Stock Option Plans (Fair Value of Stock Options) (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Common Stock Options [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 3 months	5 years	5 years
Expected volatility	45.00%	43.00%	42.40%
Risk-free interest rate	0.41%	0.32%	1.47%
Common Stock Options [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 3 months	6 years 3 months	6 years 3 months
Expected volatility	50.40%	50.30%	42.90%
Risk-free interest rate	1.08%	1.41%	2.54%
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 months	6 months
ESPP [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)			6 months
Expected volatility	46.90%	44.40%	44.40%
Risk-free interest rate	0.03%	0.10%	1.58%
ESPP [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)			7 months 17 days
Expected volatility	51.60%	76.40%	47.80%
Risk-free interest rate	0.10%	1.58%	2.45%

Stockholders' Equity (Deficit)	12 Months Ended
Stockholders' Equity (Deficit)	Dec. 31, 2021
Stockholders' Equity (Deficit) [Abstract]
Stockholders' Equity (Deficit)	9. Stockholders' Equity (Deficit) Preferred Stock At December 31, 2021, the Company’s certificate of incorporation, as amended and restated, authorizes the Company to issue up to 5,000,000 shares of preferred stock with $0.001 par value per share, of which no shares were issued and outstanding. Common Stock At December 31, 2021, the Company’s certificate of incorporation, as amended and restated, authorizes the Company to issue up to 100,000,000 shares of common stock with $0.001 par value per share, of which 34,980,896 shares were issued and outstanding. The holders of common stock are also entitled to receive dividends whenever funds are legally available, when and if declared by the Board of Directors. As of December 31, 2021, no dividends have been declared to date. Each share of common stock is entitled to one vote. At December 31, 2021 and 2020, the Company had reserved common stock for future issuances as follows: December 31, 2021 2020Exercise of options under stock plan 3,780,939 4,237,828Issuance of options and restricted stock units under stock plan 2,477,212 1,790,687Issuance of common stock under employee stock purchase plan 922,097 632,377 7,180,248 6,660,892 Common Stock Warrants In connection with the IPO, the common stock warrants were cash, or net exercised based on the IPO price of $20.00 per share into 5,968 shares of common stock. As of December 31, 2021 and 2020, the Company does not have any common stock warrants outstanding. Disgorgement Proceeds During the year ended December 31, 2021, the Company received net proceeds of $32,000 related to the disgorgement of short-swing profits under Section 16(b) of the Exchange Act. The amount was recorded as an increase to additional paid-in capital on the balance sheet.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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+ Details