CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net loss	$ (38,403)	$ (17,453)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation	7,464	2,312
Depreciation and amortization	774	722
Accretion on marketable securities	(1,413)	(209)
Amortization of debt issuance costs	259	259
Change in fair value of redeemable convertible preferred stock warrants	0	826
Loss on sale and disposal of property and equipment	171	52
Changes in operating assets and liabilities
Accounts receivable	(3,236)	(1,028)
Inventory	(2,105)	(759)
Prepaid expenses and other assets	(515)	(752)
Accounts payable	383	251
Accrued liabilities and other	4,994	1,260
Net cash used in operating activities	(31,627)	(14,519)
Cash flows from investing activities
Maturities of marketable securities	159,800	0
Purchases of marketable securities	(143,864)	(96,883)
Purchases of property and equipment	(2,445)	(942)
Net cash provided by (used in) investing activities	13,491	(97,825)
Cash flows from financing activities
Proceeds from initial public offering, net of underwriting discounts and commissions	0	115,506
Proceeds from the exercise of common stock options	1,490	1,614
Proceeds from issuance of common stock under employee stock purchase plan	2,203	0
Repurchase of unvested early exercised stock options	(38)	(73)
Payments of public offering costs	(167)	(1,897)
Net cash provided by financing activities	3,488	115,150
Effect of exchange rate changes on cash and cash equivalents	(37)	(94)
Net (decrease) increase in cash and cash equivalents	(14,685)	2,712
Cash and cash equivalents at
Beginning of year	25,120	22,408
End of year	10,435	25,120
Supplemental disclosure of cash flow information
Cash paid for interest	4,949	5,500
Supplemental disclosure of non-cash information
Conversion of redeemable convertible preferred stock to common stock	0	118,547
Conversion of preferred stock warrants to common stock warrants	0	1,248
Vesting of early exercised stock options	197	139
Purchases of property and equipment included in accounts payable and accrued liabilities	375	82
Public offering costs included in accounts payable	$ 0	$ 7