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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2020	Aug. 06, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Trading Symbol	SWAV
Entity Registrant Name	Shockwave Medical, Inc.
Entity Central Index Key	0001642545
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		34,002,860
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity File Number	001-38829
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-0494101
Entity Address, Address Line One	5403 Betsy Ross Drive
Entity Address, City or Town	Santa Clara
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	95054
City Area Code	510
Local Phone Number	279-4262
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Shockwave Medical, Inc., common stock, par value $0.001 per share
Security Exchange Name	NASDAQ

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
CURRENT ASSETS:
Cash and cash equivalents	$ 218,296	$ 139,045
Short-term investments	13,109	56,304
Accounts receivable, net	6,365	7,377
Inventory	23,427	12,074
Prepaid expenses and other current assets	3,117	1,897
Total current assets	264,314	216,697
Operating lease right-of-use assets	8,130	8,825
Property and equipment, net	13,287	4,910
Other assets	1,622	1,506
TOTAL ASSETS	287,353	231,938
CURRENT LIABILITIES:
Accounts payable	2,562	2,790
Term notes, current portion		6,667
Accrued liabilities	14,381	13,777
Lease liability, current portion	798	774
Total current liabilities	17,741	24,008
Lease liability, noncurrent portion	7,903	8,125
Term notes, noncurrent portion	16,286	7,152
TOTAL LIABILITIES	41,930	39,285
STOCKHOLDERS’ EQUITY:
Preferred stock
Common stock	34	31
Additional paid-in capital	460,235	370,561
Accumulated other comprehensive income	21	35
Accumulated deficit	(214,867)	(177,974)
TOTAL STOCKHOLDERS’ EQUITY	245,423	192,653
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 287,353	$ 231,938

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue:
Product revenue	$ 10,286	$ 10,012	$ 25,483	$ 17,282
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Cost of revenue:
Cost of product revenue	$ 3,592	$ 4,133	$ 9,243	$ 7,205
Type of Cost, Good Or Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Gross profit	$ 6,694	$ 5,879	$ 16,240	$ 10,077
Operating expenses:
Research and development	8,101	6,926	19,991	14,410
Sales and marketing	11,206	6,961	21,617	12,831
General and administrative	5,398	3,245	11,622	6,247
Total operating expenses	24,705	17,132	53,230	33,488
Loss from operations	(18,011)	(11,253)	(36,990)	(23,411)
Interest expense	(306)	(250)	(583)	(495)
Change in fair value of warrant liability				(609)
Other income, net	220	913	724	1,133
Net loss before taxes	(18,097)	(10,590)	(36,849)	(23,382)
Income tax provision	21	18	44	25
Net loss	(18,118)	(10,608)	(36,893)	(23,407)
Unrealized gain/(loss) on available-for-sale securities	(82)	75	(14)	75
Total comprehensive loss	$ (18,200)	$ (10,533)	$ (36,907)	$ (23,332)
Net loss per share, basic and diluted	$ (0.56)	$ (0.38)	$ (1.16)	$ (1.25)
Shares used in computing net loss per share, basic and diluted	32,156,476	28,002,887	31,900,259	18,735,307

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ (122,588)		$ 2	$ 4,275		$ (126,865)
Temporary equity, Beginning balance, Shares at Dec. 31, 2018		18,670,328
Temporary equity, Beginning balance at Dec. 31, 2018		$ 152,806
Beginning balance, Shares at Dec. 31, 2018			1,824,852
Exercise of common stock warrants for cash	110			110
Exercise of common stock warrants for cash, Shares			50,331
Issuance of common stock upon net exercise of warrants	133			133
Issuance of common stock upon net exercise of warrants, Shares			101,744
Conversion of preferred stock to common stock upon initial public offering	152,806		$ 18	152,788
Temporary equity, Conversion of preferred stock to common stock upon initial public offering, Shares		(18,670,328)
Temporary equity, Conversion of preferred stock to common stock upon initial public offering		$ (152,806)
Conversion of preferred stock to common stock upon initial public offering, Shares			18,670,328
Conversion of Series A-1 warrants to common stock warrants upon initial public offering	789			789
Issuance of common stock in connection with initial/public offering	100,139		$ 7	100,132
Issuance of common stock in connection with initial/public offering, Shares			6,555,000
Issuance of common stock in connection with private placement	10,000		$ 1	9,999
Issuance of common stock in connection with private placement, Shares			588,235
Exercise of stock options	169			169
Exercise of stock options, Shares			80,515
Vesting of early exercised options	18			18
Offering cost related to the initial public offering	(11,300)
Stock-based compensation	412			412
Settlement of fractional shares resulting from reverse stock split	(3)			(3)
Settlement of fractional shares resulting from reverse stock split, Shares			(114)
Net loss	(12,799)					(12,799)
Ending balance at Mar. 31, 2019	129,186		$ 28	268,822		(139,664)
Ending balance, shares at Mar. 31, 2019			27,870,891
Beginning balance at Dec. 31, 2018	(122,588)		$ 2	4,275		(126,865)
Temporary equity, Beginning balance, Shares at Dec. 31, 2018		18,670,328
Temporary equity, Beginning balance at Dec. 31, 2018		$ 152,806
Beginning balance, Shares at Dec. 31, 2018			1,824,852
Net loss	(23,407)
Ending balance at Jun. 30, 2019	119,413		$ 28	269,582	$ 75	(150,272)
Ending balance, shares at Jun. 30, 2019			28,023,707
Beginning balance at Mar. 31, 2019	129,186		$ 28	268,822		(139,664)
Beginning balance, Shares at Mar. 31, 2019			27,870,891
Issuance of common stock upon net exercise of warrants, Shares			79,208
Exercise of stock options	148			148
Exercise of stock options, Shares			73,608
Vesting of early exercised options	9			9
Unrealized gain (loss) on available-for- sale securities	75				75
Offering cost related to the initial public offering	(215)			(215)
Stock-based compensation	818			818
Net loss	(10,608)					(10,608)
Ending balance at Jun. 30, 2019	119,413		$ 28	269,582	75	(150,272)
Ending balance, shares at Jun. 30, 2019			28,023,707
Beginning balance at Dec. 31, 2019	192,653		$ 31	370,561	35	(177,974)
Beginning balance, Shares at Dec. 31, 2019			31,446,787
Exercise of stock options	1,113		$ 1	1,112
Exercise of stock options, Shares			356,128
Issuance of common stock under employee stock purchase plan	842			842
Issuance of common stock under employee stock purchase plan, Share			24,691
Unrealized gain (loss) on available-for- sale securities	68				68
Stock-based compensation	1,871			1,871
Net loss	(18,775)					(18,775)
Ending balance at Mar. 31, 2020	177,772		$ 32	374,386	103	(196,749)
Ending balance, shares at Mar. 31, 2020			31,827,606
Beginning balance at Dec. 31, 2019	$ 192,653		$ 31	370,561	35	(177,974)
Beginning balance, Shares at Dec. 31, 2019			31,446,787
Exercise of stock options, Shares	493,306
Net loss	$ (36,893)
Ending balance at Jun. 30, 2020	245,423		$ 34	460,235	21	(214,867)
Ending balance, shares at Jun. 30, 2020			33,945,557
Beginning balance at Mar. 31, 2020	177,772		$ 32	374,386	103	(196,749)
Beginning balance, Shares at Mar. 31, 2020			31,827,606
Issuance of common stock in connection with initial/public offering	83,382		$ 2	83,380
Issuance of common stock in connection with initial/public offering, Shares			1,955,000
Exercise of stock options	480			480
Exercise of stock options, Shares			137,178
Issuance of common stock in connection with vesting of restricted stock units, Shares			41,229
Restricted stock units withheld in net settlement for tax	(616)			(616)
Restricted stock units withheld in net settlement for tax, Shares			(15,456)
Unrealized gain (loss) on available-for- sale securities	(82)				(82)
Offering cost related to the initial public offering	(6,100)
Stock-based compensation	2,605			2,605
Net loss	(18,118)					(18,118)
Ending balance at Jun. 30, 2020	$ 245,423		$ 34	$ 460,235	$ 21	$ (214,867)
Ending balance, shares at Jun. 30, 2020			33,945,557

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (36,893)	$ (23,407)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	877	516
Stock-based compensation	4,262	1,230
Amortization of right-of-use assets	734	496
Accretion of discount on available-for-sale securities	201	(354)
Loss on write down of fixed assets		88
Change in fair value of warrant liability		609
Amortization of debt issuance costs	313	212
Changes in operating assets and liabilities:
Accounts receivable	1,012	(2,392)
Inventory	(10,965)	(3,160)
Prepaid expenses and other current assets	(1,220)	(841)
Other assets	(116)	5
Accounts payable	(282)	713
Accrued and other current liabilities	(41)	1,848
Lease liabilities	(237)	(496)
Net cash used in operating activities	(42,355)	(24,933)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of available-for-sale securities	(16,020)	(82,784)
Proceeds from maturities of available-for-sale securities	59,000
Purchase of property and equipment	(8,952)	(1,191)
Net cash provided by (used in) investing activities	34,028	(83,975)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock upon initial public offering, net of issuance costs paid		100,762
Proceeds from issuance of common stock in private placement		10,000
Payments of offering costs	(179)
Proceed from issuance of common stock from public offering, net of issuance cost paid	83,784
Payments of taxes withheld on net settled vesting of restricted stock units	(616)
Principal payments of term loan	(1,111)
Net proceeds from term loan	3,265
Proceeds from stock option exercises	1,593	317
Proceeds from issuance of common stock under employee stock purchase plan	842
Proceeds from warrant exercises		110
Net cash provided by financing activities	87,578	111,189
Net increase in cash, cash equivalents and restricted cash	79,251	2,281
Cash, cash equivalents and restricted cash at beginning of period	140,495	40,093
Cash, cash equivalents and restricted cash equivalents at end of period	219,746	42,374
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest paid	256	276
Income tax paid	10	8
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Common stock issued on conversion of convertible preferred stock		152,806
Common stock issued upon net exercise of warrants		133
Common stock warrants issued on conversion of preferred stock warrants and the reclassification of the warrant liability		789
Offering costs included in accounts payable and accrued liabilities	402	215
Right-of-use asset obtained in exchange for lease liability	39	73
Property and equipment purchases included in accounts payable and accrued liabilities	501	$ 93
Transfer of fixed assets to inventory	$ 174

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and applicable rules and regulations of SEC regarding interim financial reporting.

The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s consolidated financial position, results of operations and cash flows. The results of operations for the six months ended June 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2019 included herein was derived from the audited financial statements as of that date. The unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019, filed with the SEC on March 12, 2020.

Reclassifications

Certain amounts in the prior period condensed consolidated financial statements have been reclassified to conform to the current period presentation.

Cash, Cash Equivalents, and Restricted Cash

The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts.

Restricted cash as of June 30, 2020 and December 31, 2019 relates to a letter of credit established for the Company’s office lease and is recorded as other assets on the condensed consolidated balance sheets.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same amounts shown in the condensed consolidated statements of cash flows:

	June 30, 2020		December 31, 2019
	(in thousands)
Cash and cash equivalents	$	218,296	$	139,045
Restricted cash		1,450		1,450
Total cash, cash equivalents, and restricted cash	$	219,746	$	140,495

Short-Term Investments

Short-term investments have been classified as available-for-sale and are carried at estimated fair value based upon quoted market prices or pricing models for similar securities. The Company determines the appropriate classification of its investments in debt securities at the time of purchase. Available-for-sale securities with original maturities beyond three months at the date of purchase are classified as current based on their availability for use in current operations.

Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss, except for credit-related impairment losses. The Company periodically evaluates whether declines in fair values of its marketable securities below their book value are other-than-temporary and if they are related to deterioration in credit risk. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the marketable security until a forecasted recovery occurs. The Company also assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any marketable securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on marketable securities are included in other income, net. Effective January 1, 2020, any unrealized losses on available-for-sale debt securities that are attributed to credit risk are recorded to earnings through an allowance for credit losses. The cost of investments sold is based on the specific-identification method. Interest on marketable securities is included in other income, net.

Fair Value of Financial Instruments

The Company’s cash and cash equivalents, restricted cash, short-term investments, accounts receivable, accounts payable and accrued liabilities approximate their fair value due to their short maturities. Management believes that its term notes bear interest at the prevailing market rates for instruments with similar characteristics; accordingly, the carrying value of this instrument approximates its fair value.

The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines the fair value of its financial instruments based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels:

Level 1 – Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

Level 2 – Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

Level 3 – Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.

Revenue

The Company records product revenue primarily from the sale of its IVL catheters. The Company sells its products to hospitals, primarily through direct sales representatives, as well as through distributors in selected international markets. Additionally, a significant portion of the Company’s revenue is generated through a consignment model under which inventory is maintained at hospitals.

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.

For products sold through direct sales representatives, control is transferred upon delivery to customers. For products sold to distributors internationally and products sold to customers that utilize stocking orders, control is transferred upon shipment or delivery to the customer’s named location, based on the contractual shipping terms. For consignment inventory, control is transferred at the time the IVL catheters are consumed in a procedure.

In the United States the Company generally provides for the use of an IVL generator and connector cable under an agreement to customers at no charge to facilitate use of the IVL catheters. These agreements do not contain contractually enforceable minimum commitments and are generally cancellable by either party with 30 days’ notice.

Recently Adopted Accounting Pronouncements

Effective January 1, 2020, the Company adopted ASU No. 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. Unrealized losses on available-for-sale debt securities that are attributed to credit risk are recorded through earnings rather than to other comprehensive income. Credit losses relating to available-for-sale debt securities are now recorded through an allowance for credit losses. The adoption of this guidance did not result in a cumulative effect adjustment as of the date of the adoption.

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. During the six months ended June 30, 2020, the Company recorded an additional allowance for bad debt in response to an assessment of the evolving credit environment under the COVID-19 pandemic. The Company will continue to update its estimate of credit losses from accounts receivable in future periods in response to the uncertainties caused by the COVID-19 pandemic.

Financial Instruments and Fair Value Measurements

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Financial Instruments and Fair Value Measurements

3. Financial Instruments and Fair Value Measurements

The following tables summarize the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy:

	June 30, 2020
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
U.S. Treasury securities	$	10,063	$	—	$	—	$	10,063
Money market funds		135,214		—		—		135,214
Corporate bonds		—		3,046		—		3,046
Total assets	$	145,277	$	3,046	$	—	$	148,323

	December 31, 2019
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
U.S. Treasury securities	$	43,245	$	—	$	—	$	43,245
Money market funds		29,386		—		—		29,386
Reverse repurchase agreements		—		10,000		—		10,000
Commercial paper		—		6,958		—		6,958
Corporate bonds		—		8,096		—		8,096
Total assets	$	72,631	$	25,054	$	—	$	97,685

The Company’s convertible preferred stock warrants were converted into common stock warrants upon the closing of an initial public offering of the Company’s common stock (“IPO”) in March 2019. The change in the fair value of the warrant liability for the three months ended March 31, 2019 is summarized below (in thousands):

Balance at December 31, 2018	$	313
Change in fair value of warrant liability		609
Net exercise of warrants		(133	)
Conversion of Series A preferred stock warrants to common stock warrants upon the closing of the IPO		(789	)
Balance at March 31, 2019	$	—

The valuation of the Company’s convertible preferred stock warrant liability contains unobservable inputs that reflect the Company’s own assumptions for which there is little, if any, market activity for at the measurement date. Accordingly, the Company’s convertible preferred stock warrant liability is measured at fair value on a recurring basis using unobservable inputs and are classified as Level 3 inputs, and any change in fair value is recognized as change in fair value of warrant liability in the condensed consolidated statements of operations and comprehensive loss.

The fair value of the warrants was determined using the Black-Scholes option pricing model and the following assumptions:

	March 31, 2019
Expected term (in years)		5.3
Expected volatility	43.9%
Risk-free interest rate	2.5%
Expected dividend yield	0%

- 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

Cash Equivalents and Short-Term Investments

6 Months Ended

Jun. 30, 2020

Cash And Cash Equivalents [Abstract]

Cash Equivalents and Short-Term Investments

4. Cash Equivalents and Short-Term Investments

The following is a summary of the Company’s cash equivalents and short-term investments:

	June 30, 2020
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses		Fair Value
	(in thousands)
U.S. Treasury securities	$	10,043	$	20	$	—	$	10,063
Money market funds		135,214		—		—		135,214
Corporate bonds		3,045		1		—		3,046
Total	$	148,302	$	21	$	—	$	148,323
Reported as:
Cash equivalents							$	135,214
Short-term investments								13,109
Total							$	148,323

	December 31, 2019
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
U.S. Treasury securities	$	43,219	$	27	$	(1	)	$	43,245
Money market funds		29,386		—		—			29,386
Reverse repurchase agreements		10,000		—		—			10,000
Commercial paper		6,958		—		—			6,958
Corporate bonds		8,087		9		—			8,096
Total	$	97,650	$	36	$	(1	)	$	97,685
Reported as:
Cash equivalents								$	41,381
Short-term investments									56,304
Total								$	97,685

The Company recognized no material gains or losses on its cash equivalents and short-term investments in the periods presented. As of June 30, 2020, the remaining contractual maturities for available-for-sale securities were less than one year.

Balance Sheet Components

6 Months Ended

Jun. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Components

5. Balance Sheet Components

Inventory

Inventory consists of the following:

	June 30,		December 31,
	2020		2019
	(in thousands)
Raw material	$	4,138	$	2,501
Work in progress		2,682		1,364
Finished goods		14,850		6,642
Consigned inventory		1,757		1,567
Total inventory	$	23,427	$	12,074

Accrued Liabilities

Accrued liabilities consist of the following:

	June 30,		December 31,
	2020		2019
	(in thousands)
Accrued employee compensation	$	7,300	$	8,139
Accrued asset purchases		633		—
Accrued research and development costs		3,734		3,090
Accrued professional services		1,152		804
Other		1,562		1,744
Total accrued liabilities	$	14,381	$	13,777

Term Notes

6 Months Ended

Jun. 30, 2020

Debt Disclosure [Abstract]

Term Notes

6. Term Notes

Loan and Security Agreement

In February 2018, the Company entered into a Loan and Security Agreement with Silicon Valley Bank (the “Loan and Security Agreement”). The terms of the Loan and Security Agreement included a term loan of $15.0 million and a revolving line of credit of $2.0 million. The term loan was available in two tranches, of which the first tranche of $10.0 million was funded in June 2018 and the second tranche of $5.0 million was funded in December 2018.

The term loan accrued interest at a floating per annum rate equal to the greater of the Wall Street Journal prime rate minus 1.75% and 2.75%. There was a final payment equal to 6.75% of the original aggregate principal amount, or $1.0 million, of the term loan advances, which was being accrued over the expected term of the loan using the effective-interest method.

In connection with the execution of the Loan and Security Agreement, the Company issued warrants to Silicon Valley Bank to purchase 34,440 shares of the Company’s common stock. Upon issuance, the fair value of the warrants of $0.1 million was recorded as a debt issuance cost. The debt issuance cost was being amortized to interest expense, net over the expected repayment period of the loan.

In February 2020, the Company entered into a First Amendment to its Loan and Security Agreement (the “Amended Credit Facility”) to, among other things, refinance its existing term loan, which is accounted for as a modification of the Loan and Security Agreement. Under the Amended Credit Facility, the existing revolving line of credit of $2.0 million was terminated and the termination fee of less than $0.1 million was waived. The Amended Credit Facility provides the Company with a supplemental term loan in the amount of $16.5 million. After repayment of the outstanding amount of the term loan, the Company received net proceeds of $3.3 million, which reflects an additional $4.3 million in principal as of the date of the modification less the final balloon payment fee of $1.0 million. The principal amount outstanding under the supplemental term loan accrues interest at a floating per annum rate equal to the greater of the Prime Rate minus 1.25% and 3.5% (3.5% as of June 30, 2020).

The supplemental term loan matures on December 1, 2023. The Amended Credit Facility provides an interest-only payment period which will end on (a) June 30, 2021, if the Company’s revenue for the trailing 12 month period ended June 30, 2021 is not at least 75% of the Company’s projections; (b) December 31, 2021, if the Company achieves the financial performance target referred to in clause (a), but does not obtain premarket approval of the Company’s C²catheters from the FDA by such date and/or the Company’s trailing 12-month revenue for the period ending December 31, 2021 is not at least 75% of the Company’s projections; or (c) June 30, 2022, if the Company achieves the milestones referred to in clauses (a) and (b).

The additional final payment for the Amended Credit Facility is $1.6 million, which will be accrued over the term of the supplemental term loan using an effective interest rate that reflects the revised cash flows of the modified term loan.

The supplemental term loan is secured by all of the Company’s assets, excluding intellectual property and certain other assets. The loan contains customary affirmative and restrictive covenants, including with respect to the Company’s ability to enter into fundamental transactions, incur additional indebtedness, grant liens, pay any dividend or make any distributions to its holders, make investments, merge or consolidate with any other person or engage in transactions with the Company’s affiliates, but does not include any financial covenants.

Long-term debt and net discount or premium balances are as follows:

	June 30,			December 31,
	2020			2019
	(in thousands)
Principal amount of term note	$	16,500		$	13,334
Net (discount) premium associated with accretion of final payment, issuance of common stock warrants, and other debt issuance costs		(214	)		485
Term note, current and noncurrent		16,286			13,819
Less term note, current portion		—			(6,667	)
Term note, noncurrent portion	$	16,286		$	7,152

Future minimum payments of principal and estimated payments of interest on the Company’s outstanding variable rate borrowings as of June 30, 2020 are as follows:

Year ending December 31:	(in thousands)
2020 (remainder)	$	294
2021		3,861
2022		6,961
2023		8,294
Total future payments		19,410
Less amounts representing interest		(1,342	)
Less final payment		(1,568	)
Total principal amount of term note payments	$	16,500

Stock-Based Compensation

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

7. Stock-Based Compensation

Total stock-based compensation was as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(in thousands)				(in thousands)
Cost of product revenue	$	39	$	48	$	141	$	75
Research and development		650		204	$	1,138		276
Sales and marketing		837		201	$	1,396		309
General and administrative		924		365	$	1,587		570
Total stock-based compensation	$	2,450	$	818	$	4,262	$	1,230

Determination of Fair Value

The Company estimates the grant-date fair value of the Company’s option awards using the Black-Scholes option pricing model. The assumptions for the Black-Scholes model for the six months ended June 30, 2020 and 2019 were as follows:

	Six Months Ended June 30,
	2020		2019
Expected term (in years)		—	6.08
Expected volatility		—	42.4% - 42.9%
Risk-free interest rate		—	2.5% - 2.6%
Expected dividend yield		—	0%

2009 Equity Incentive Plan and 2019 Equity Incentive Plan

On June 17, 2009, the Company adopted the 2009 Equity Incentive Plan (the “2009 Plan”) under which the Board had the authority to issue stock options to employees, directors and consultants.

In February 2019, the Company adopted the 2019 Equity Incentive Plan (the “2019 Plan”), which became effective in connection with the IPO. As a result, effective as of March 6, 2019, the Company may not grant any additional awards under the 2009 Plan. The 2009 Plan will continue to govern outstanding equity awards granted thereunder. The Company initially reserved 2,000,430 shares of common stock for the issuance of a variety of awards under the 2019 Plan, including stock options, stock appreciation rights, awards of restricted stock and awards of restricted stock units. In addition, the number of shares of common stock reserved for issuance under the 2019 Plan will automatically increase on the first day of January for a period of up to ten years, commencing on January 1, 2020, in an amount equal to 3% of the total number of shares of the Company’s capital stock outstanding on the last day of the preceding year, or a lesser number of shares determined by the Company’s Board of Directors. As of June 30, 2020, there were 2,671,201 shares available for issuance under the 2019 Plan.

Stock Options

Option activity under the 2009 Plan and 2019 Plan is set forth below:

	Shares Available for Grant		Number of Shares			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Term		Aggregate Intrinsic Value
								(in years)		(in thousands)
Balance, December 31, 2019		1,704,244		3,315,001		$	5.08		7.28	$	128,774
Awards authorized		943,345		—
Options exercised		—		(493,306	)		3.23
Options forfeited		23,612		(23,612	)		3.95
Balance, June 30, 2020		2,671,201		2,798,083		$	5.42		7.17	$	117,380
Vested and exercisable, June 30, 2020				1,693,886		$	4.18		6.75	$	73,156
Vested and expected to vest, June 30, 2020				2,798,083		$	5.42		7.17	$	117,380

Restricted Stock Units

Restricted stock units (“RSUs”) are share awards that entitle the holder to receive freely tradable shares of the Company’s common stock upon vesting. The RSUs cannot be transferred and the awards are subject to forfeiture if the holder’s employment terminates prior to the release of the vesting restrictions. The RSUs generally vest over a four-year period with straight-line annual vesting, provided the employee remains continuously employed with the Company. The fair value of the RSUs is equal to the closing price of the Company’s common stock on the grant date.

RSU activity under the 2019 Plan is set forth below:

	Number of Shares			Weighted- Average Grant Date Fair Value Per Share
Balance, December 31, 2019		280,904		$	38.12
RSUs granted		517,515			42.40
RSUs vested		(41,229	)		36.25
RSUs forfeited		(13,750	)		40.40
Balance, June 30, 2020		743,440		$	41.16

Employee Stock Purchase Plan

In February 2019, the Company adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective as of March 6, 2019. The Company initially reserved 300,650 shares of common stock for purchase under the ESPP. Each offering period during which participating employees may purchase stock under the ESPP begins on each September 1 and March 1 and ends on the following February 28 or 29 and August 30, respectively. The first offering period began on September 1, 2019 and ended on February 29, 2020. On each purchase date, which falls on the last date of each offering period, ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of (1) the fair market value per share of the common stock on the offering date or (2) the fair market value of the common stock on the purchase date. The occurrence and duration of offering periods under the ESPP are subject to the determinations of the Compensation Committee of the Company’s Board of Directors, in its sole discretion.

The fair value of the ESPP shares is estimated using the Black-Scholes option pricing model. The Company recorded $207,000 and $398,000 of stock-based compensation expense related to the ESPP for the three and six months ended June 30, 2020, respectively. At June 30, 2020, a total of 590,407 shares were available for issuance under the ESPP.

Segment and Geographic Information

6 Months Ended

Jun. 30, 2020

Segment Reporting [Abstract]

Segment and Geographic Information

9. Segment and Geographic Information

The following table represents the Company’s product revenue based on the location to which the product is shipped:

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(in thousands)				(in thousands)
United States	$	5,537	$	5,172	$	13,306	$	8,808
Germany		825		873		1,736		1,516
Rest of Europe		3,107		3,309		8,215		6,045
All other countries		817		658		2,226		913
Product revenue	$	10,286	$	10,012	$	25,483	$	17,282

As of June 30, 2020 and 2019, the Company’s long-lived assets were all held in the United States with the exception of certain equipment on loan to customers held internationally, which was not material as of each period end.

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8981-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8721-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8844-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8657-108599

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8721-108599

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-URI http://asc.fasb.org/topic&trid=2134510

+ Details

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2020

Accounting Policies [Abstract]

Risk and Uncertainties

The Company is subject to risks and uncertainties as a result of the ongoing effects of the COVID-19 pandemic. There are many uncertainties regarding the current COVID-19 pandemic, and the Company is continuing to closely monitor the impact of the pandemic on all aspects of its business, including how it is impacting and how it may continue to impact its customers, patients that would benefit from procedures utilizing the Company’s products, employees, suppliers, vendors, business partners and distribution channels. The capital markets and economies worldwide continue to be negatively impacted by the COVID-19 pandemic, including U.S. and global economic recessions. As such the Company's future results of operations and liquidity may continue to be adversely impacted by a variety of factors related to the COVID-19 pandemic, including those discussed or referred to in the section entitled “Risk Factors” of this Quarterly Report on Form 10-Q.

As of the date of issuance of these condensed consolidated financial statements, the extent to which the COVID-19 pandemic may materially impact the Company's financial condition, liquidity, or results of operations is uncertain. Given the ongoing uncertainty of the scope and duration of the COVID-19 pandemic, the Company is currently unable to accurately estimate the scale and duration of the impact on its business, including procedure volumes, clinical activities and product development, and by extension the Company’s financial results.

Basis of Presentation

Reclassifications

Certain amounts in the prior period condensed consolidated financial statements have been reclassified to conform to the current period presentation.

Cash, Cash Equivalents and Restricted Cash

Cash, Cash Equivalents, and Restricted Cash

	June 30, 2020		December 31, 2019
	(in thousands)
Cash and cash equivalents	$	218,296	$	139,045
Restricted cash		1,450		1,450
Total cash, cash equivalents, and restricted cash	$	219,746	$	140,495

Short-Term Investments

Fair Value of Financial Instruments

Level 1 – Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

Level 3 – Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.

Revenue

Recently Adopted Accounting Pronouncements

Financial Instruments and Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Liabilities Measured at Fair Value

The following tables summarize the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy:

	June 30, 2020
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
U.S. Treasury securities	$	10,063	$	—	$	—	$	10,063
Money market funds		135,214		—		—		135,214
Corporate bonds		—		3,046		—		3,046
Total assets	$	145,277	$	3,046	$	—	$	148,323

	December 31, 2019
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
U.S. Treasury securities	$	43,245	$	—	$	—	$	43,245
Money market funds		29,386		—		—		29,386
Reverse repurchase agreements		—		10,000		—		10,000
Commercial paper		—		6,958		—		6,958
Corporate bonds		—		8,096		—		8,096
Total assets	$	72,631	$	25,054	$	—	$	97,685

Schedule of Change in the Fair Value of the Warrant Liability

Balance at December 31, 2018	$	313
Change in fair value of warrant liability		609
Net exercise of warrants		(133	)
Conversion of Series A preferred stock warrants to common stock warrants upon the closing of the IPO		(789	)
Balance at March 31, 2019	$	—

Fair Value of Warrants Using Black-Scholes Option Pricing Model

The fair value of the warrants was determined using the Black-Scholes option pricing model and the following assumptions:

	March 31, 2019
Expected term (in years)		5.3
Expected volatility	43.9%
Risk-free interest rate	2.5%
Expected dividend yield	0%

Cash Equivalents and Short-Term Investments (Tables)

6 Months Ended

Jun. 30, 2020

Cash And Cash Equivalents [Abstract]

Summary of Cash Equivalents and Short-Term Investments

The following is a summary of the Company’s cash equivalents and short-term investments:

	June 30, 2020
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses		Fair Value
	(in thousands)
U.S. Treasury securities	$	10,043	$	20	$	—	$	10,063
Money market funds		135,214		—		—		135,214
Corporate bonds		3,045		1		—		3,046
Total	$	148,302	$	21	$	—	$	148,323
Reported as:
Cash equivalents							$	135,214
Short-term investments								13,109
Total							$	148,323

	December 31, 2019
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
U.S. Treasury securities	$	43,219	$	27	$	(1	)	$	43,245
Money market funds		29,386		—		—			29,386
Reverse repurchase agreements		10,000		—		—			10,000
Commercial paper		6,958		—		—			6,958
Corporate bonds		8,087		9		—			8,096
Total	$	97,650	$	36	$	(1	)	$	97,685
Reported as:
Cash equivalents								$	41,381
Short-term investments									56,304
Total								$	97,685

Balance Sheet Components (Tables)

6 Months Ended

Jun. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Inventory

Inventory consists of the following:

	June 30,		December 31,
	2020		2019
	(in thousands)
Raw material	$	4,138	$	2,501
Work in progress		2,682		1,364
Finished goods		14,850		6,642
Consigned inventory		1,757		1,567
Total inventory	$	23,427	$	12,074

Schedule of Accrued Liabilities

Accrued liabilities consist of the following:

	June 30,		December 31,
	2020		2019
	(in thousands)
Accrued employee compensation	$	7,300	$	8,139
Accrued asset purchases		633		—
Accrued research and development costs		3,734		3,090
Accrued professional services		1,152		804
Other		1,562		1,744
Total accrued liabilities	$	14,381	$	13,777

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Total Stock-Based Compensation

Total stock-based compensation was as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(in thousands)				(in thousands)
Cost of product revenue	$	39	$	48	$	141	$	75
Research and development		650		204	$	1,138		276
Sales and marketing		837		201	$	1,396		309
General and administrative		924		365	$	1,587		570
Total stock-based compensation	$	2,450	$	818	$	4,262	$	1,230

Schedule of Estimates Grant-Date Fair Value of Option Awards Using Black-Scholes Option Pricing Model with Assumptions

	Six Months Ended June 30,
	2020		2019
Expected term (in years)		—	6.08
Expected volatility		—	42.4% - 42.9%
Risk-free interest rate		—	2.5% - 2.6%
Expected dividend yield		—	0%

Schedule of Option Activity under 2009 Plan and 2019 Plan

Stock Options

Option activity under the 2009 Plan and 2019 Plan is set forth below:

	Shares Available for Grant		Number of Shares			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Term		Aggregate Intrinsic Value
								(in years)		(in thousands)
Balance, December 31, 2019		1,704,244		3,315,001		$	5.08		7.28	$	128,774
Awards authorized		943,345		—
Options exercised		—		(493,306	)		3.23
Options forfeited		23,612		(23,612	)		3.95
Balance, June 30, 2020		2,671,201		2,798,083		$	5.42		7.17	$	117,380
Vested and exercisable, June 30, 2020				1,693,886		$	4.18		6.75	$	73,156
Vested and expected to vest, June 30, 2020				2,798,083		$	5.42		7.17	$	117,380

Schedule of RSU Activity under 2019 Plan

RSU activity under the 2019 Plan is set forth below:

	Number of Shares			Weighted- Average Grant Date Fair Value Per Share
Balance, December 31, 2019		280,904		$	38.12
RSUs granted		517,515			42.40
RSUs vested		(41,229	)		36.25
RSUs forfeited		(13,750	)		40.40
Balance, June 30, 2020		743,440		$	41.16

Cash Equivalents and Short-Term Investments - Summary of Cash Equivalents and Short-Term Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Cash And Cash Equivalents [Line Items]
Cash equivalents, Fair Value	$ 135,214	$ 41,381
Cash equivalents and short-term investments, Amortized Cost Basis	148,302	97,650
Cash equivalents and short-term investments, Unrealized Gains	21	36
Cash equivalents and short-term investments, Unrealized losses		(1)
Cash equivalents and short-term investments, Fair Value	148,323	97,685
Short-term investments	13,109	56,304
U.S. Treasury securities
Cash And Cash Equivalents [Line Items]
Short-term investments Amortized Cost Basis	10,043	43,219
Short-term investments Unrealized Gains	20	27
Short-term investments Unrealized Losses		(1)
Short-term investments, Fair Value	10,063	43,245
Reverse Repurchase Agreements
Cash And Cash Equivalents [Line Items]
Short-term investments Amortized Cost Basis		10,000
Short-term investments, Fair Value		10,000
Corporate bonds
Cash And Cash Equivalents [Line Items]
Short-term investments Amortized Cost Basis	3,045	8,087
Short-term investments Unrealized Gains	1	9
Short-term investments, Fair Value	3,046	8,096
Commercial paper
Cash And Cash Equivalents [Line Items]
Short-term investments Amortized Cost Basis		6,958
Short-term investments, Fair Value		6,958
Money Market Funds
Cash And Cash Equivalents [Line Items]
Cash equivalents Amortized Cost Basis	135,214	29,386
Cash equivalents, Fair Value	$ 135,214	$ 29,386

Term Notes - Additional Information (Detail) - USD ($)		6 Months Ended
Term Notes - Additional Information (Detail) - USD ($)	Feb. 29, 2020	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Feb. 28, 2018
Debt Instrument [Line Items]
Debt Amount		$ 16,500,000	$ 13,334,000
Debt, final payment amount		$ 1,568,000
Loan and Security Agreement
Debt Instrument [Line Items]
Debt, final payment as percentage of original aggregate principal amount		6.75%
Debt, final payment amount		$ 1,600,000				$ 1,000,000
Proceeds of supplemental term loan	$ 4,300,000
Debt payments description		The Amended Credit Facility provides an interest-only payment period which will end on (a) June 30, 2021, if the Company’s revenue for the trailing 12 month period ended June 30, 2021 is not at least 75% of the Company’s projections; (b) December 31, 2021, if the Company achieves the financial performance target referred to in clause (a), but does not obtain premarket approval of the Company’s C2 catheters from the FDA by such date and/or the Company’s trailing 12-month revenue for the period ending December 31, 2021 is not at least 75% of the Company’s projections; or (c) June 30, 2022, if the Company achieves the milestones referred to in clauses (a) and (b).
Loan and Security Agreement \| Supplemental Term Loan
Debt Instrument [Line Items]
Debt Amount	16,500,000
Debt interest rate		3.50%
Proceeds of supplemental term loan, net of final balloon payment fee	$ 3,300,000
Debt maturity date	Dec. 01, 2023
Loan and Security Agreement \| Interest Payment End On June 30, 2021
Debt Instrument [Line Items]
Debt instrument percentage of projected revenue to be achieved	75.00%
Loan and Security Agreement \| Interest Payment End On December 31, 2021
Debt Instrument [Line Items]
Debt instrument percentage of projected financial performance target	75.00%
Loan and Security Agreement \| Minimum
Debt Instrument [Line Items]
Debt interest rate		1.75%
Loan and Security Agreement \| Minimum \| Prime Rate \| Supplemental Term Loan
Debt Instrument [Line Items]
Debt interest rate basis	1.25%
Loan and Security Agreement \| Maximum
Debt Instrument [Line Items]
Debt interest rate basis		2.75%
Loan and Security Agreement \| Maximum \| Supplemental Term Loan
Debt Instrument [Line Items]
Debt interest rate	3.50%
Loan and Security Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Termination of line of credit facility	$ 2,000,000
Loan and Security Agreement \| Revolving Credit Facility \| Maximum
Debt Instrument [Line Items]
Line of credit facility termination fee	$ 100,000
Loan and Security Agreement \| Silicon Valley Bank
Debt Instrument [Line Items]
Debt, warrants issued		34,440
Debt, fair value of warrants issued		$ 100,000
Loan and Security Agreement \| Silicon Valley Bank \| Short Term Notes
Debt Instrument [Line Items]
Debt Amount						15,000,000
Loan and Security Agreement \| Silicon Valley Bank \| Short Term Notes \| Tranche One
Debt Instrument [Line Items]
Debt Amount					$ 10,000,000
Loan and Security Agreement \| Silicon Valley Bank \| Short Term Notes \| Tranche Two
Debt Instrument [Line Items]
Debt Amount				$ 5,000,000
Loan and Security Agreement \| Silicon Valley Bank \| Revolving Credit Facility
Debt Instrument [Line Items]
Debt Amount						$ 2,000,000

Stock-Based Compensation - Schedule of Option Activity under 2009 Plan and 2019 Plan (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Shares Available for Grant
Shares Available for Grant, Beginning balance	1,704,244
Shares Available for Grant, Awards authorized	943,345
Shares Available for Grant, Options forfeited	23,612
Shares Available for Grant, Ending balance	2,671,201	1,704,244
Number of Shares
Number of Shares, Beginning balance	3,315,001
Number of Shares, Options exercised	(493,306)
Number of Shares, Options forfeited	(23,612)
Number of Shares, Ending balance	2,798,083	3,315,001
Number of Shares, Vested and exercisable	1,693,886
Number of Shares, Vested and expected to vest	2,798,083
Weighted-Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Beginning balance \| $ / shares	$ 5.08
Weighted-Average Exercise Price Per Share, Options exercised \| $ / shares	3.23
Weighted-Average Exercise Price Per Share, Options forfeited \| $ / shares	3.95
Weighted-Average Exercise Price Per Share, Ending balance \| $ / shares	5.42	$ 5.08
Weighted-Average Exercise Price Per Share, Vested and exercisable \| $ / shares	4.18
Weighted-Average Exercise Price Per Share, Vested and expected to vest \| $ / shares	$ 5.42
Weighted-Average Remaining Term
Weighted-Average Remaining Term, Balance	7 years 2 months 1 day	7 years 3 months 10 days
Weighted-Average Remaining Term, Vested and exercisable	6 years 9 months
Weighted-Average Remaining Term, Vested and expected to vest	7 years 2 months 1 day
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Balance \| $	$ 117,380	$ 128,774
Aggregate Intrinsic Value, Vested and exercisable \| $	73,156
Aggregate Intrinsic Value, Vested and expected to vest \| $	$ 117,380

Stock-Based Compensation - Schedule of RSU Activity under 2019 Plan (Detail) - Restricted Stock Units	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Number of Shares
Number of Shares, Beginning balance \| shares	280,904
Number of Shares, RSUs granted \| shares	517,515
Number of Shares, RSUs vested \| shares	(41,229)
Number of Shares, RSUs forfeited \| shares	(13,750)
Number of Shares, Ending balance \| shares	743,440
Weighted-Average Grant Date Fair Value Per Share
Weighted-Average Grant Date Fair Value Per Share, Beginning balance \| $ / shares	$ 38.12
Weighted-Average Grant Date Fair Value Per Share, RSUs granted \| $ / shares	42.40
Weighted-Average Grant Date Fair Value Per Share, RSUs vested \| $ / shares	36.25
Weighted-Average Grant Date Fair Value Per Share, RSUs forfeited \| $ / shares	40.40
Weighted-Average Grant Date Fair Value Per Share, Ending balance \| $ / shares	$ 41.16

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019
Statement Of Stockholders Equity [Abstract]
Issuance costs	$ 6,100	$ 215	$ 11,300

Financial Instruments and Fair Value Measurements - Fair Value of Warrants Using Black-Scholes Option Pricing Model (Details)	Mar. 31, 2019
Measurement Input, Expected Term
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected term (in years)	5 years 3 months 18 days
Measurement Input, Expected Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value assumption measurement input	43.9
Measurement Input, Risk-free Interest Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value assumption measurement input	2.5
Measurement Input, Expected Dividend Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value assumption measurement input	0

Stock-Based Compensation - Schedule of Estimates Grant-Date Fair Value of Option Awards Using Black-Scholes Option Pricing Model with Assumptions (Detail)	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected term (in years)	6 years 29 days
Expected volatility, minimum	42.40%
Expected volatility, maximum	42.90%
Risk-free interest rate, minimum	2.50%
Risk-free interest rate, maximum	2.60%
Expected dividend yield	0.00%

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended	6 Months Ended
	Mar. 31, 2019	Feb. 28, 2019	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for issuance			2,671,201	2,671,201		1,704,244
Stock-based compensation				$ 4,262,000	$ 1,230,000
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period				4 years
Share-based compensation vesting rights, terms				The RSUs generally vest over a four-year period with straight-line annual vesting,
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance		2,000,430
Maximum period of automatic annual increase in common stock reserved for issuance		10 years
Automatic annual increase in common stock reserved for issuance		3.00%
Shares available for issuance			2,671,201	2,671,201
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance	300,650
Shares available for issuance			590,407	590,407
Purchase shares of common stock, price per share, percentage of fair market value	85.00%
Stock-based compensation			$ 207,000	$ 398,000

Net Loss Per Share - Summary of Outstanding Potentially Dilutive Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	3,541,523	4,070,110
Common Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	2,798,083	3,896,360
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	743,440	173,750

Summary of Significant Accounting Policies - Additional Information (Details)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Notice period for cancellation of agreement	30 days

Financial Instruments and Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Total assets	$ 148,323	$ 97,685
U.S. Treasury securities
Assets:
Total assets	10,063	43,245
Money Market Funds
Assets:
Total assets	135,214	29,386
Reverse Repurchase Agreements
Assets:
Total assets		10,000
Commercial paper
Assets:
Total assets		6,958
Corporate bonds
Assets:
Total assets	3,046	8,096
Level 1
Assets:
Total assets	145,277	72,631
Level 1 \| U.S. Treasury securities
Assets:
Total assets	10,063	43,245
Level 1 \| Money Market Funds
Assets:
Total assets	135,214	29,386
Level 2
Assets:
Total assets	3,046	25,054
Level 2 \| Reverse Repurchase Agreements
Assets:
Total assets		10,000
Level 2 \| Commercial paper
Assets:
Total assets		6,958
Level 2 \| Corporate bonds
Assets:
Total assets	$ 3,046	$ 8,096

Financial Instruments and Fair Value Measurements - Schedule of Change in the Fair Value of the Warrant Liability (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Fair Value Disclosures [Abstract]
Balance at December 31, 2018	$ 313
Change in fair value of warrant liability	609
Net exercise of warrants	(133)
Conversion of Series A preferred stock warrants to common stock warrants upon the closing of the IPO	$ (789)

Cash Equivalents and Short-Term Investments - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2020
Maximum
Cash And Cash Equivalents [Line Items]
Available for sale securities remaining contractual maturities	1 year

Balance Sheet Components - Schedule of Inventory (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw material	$ 4,138	$ 2,501
Work in progress	2,682	1,364
Finished goods	14,850	6,642
Consigned inventory	1,757	1,567
Total inventory	$ 23,427	$ 12,074

Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued employee compensation	$ 7,300	$ 8,139
Accrued asset purchases	633
Accrued research and development costs	3,734	3,090
Accrued professional services	1,152	804
Other	1,562	1,744
Total accrued liabilities	$ 14,381	$ 13,777

Term Notes - Long-term Debt and Net Premium Balance (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument Periodic Payment [Abstract]
Principal amount of term note	$ 16,500	$ 13,334
Net (discount) premium associated with accretion of final payment, issuance of common stock warrants, and other debt issuance costs	(214)	485
Term note, current and noncurrent	16,286	13,819
Less term note, current portion		(6,667)
Term note, noncurrent portion	$ 16,286	$ 7,152