CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net loss	$ (43,697)	$ (38,403)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation	11,927	7,464
Depreciation and amortization	1,130	774
Bad debt expense	234	0
Accretion of discount on marketable securities	115	(1,413)
Realized gain on marketable securities	(46)	0
Amortization of debt issuance costs	292	259
Loss on extinguishment of debt	1,534	0
Loss on sale and disposal of property and equipment	376	171
Changes in operating assets and liabilities
Accounts receivable	(2,186)	(3,236)
Inventory	(274)	(2,105)
Prepaid expenses and other assets	(136)	(515)
Accounts payable	835	383
Accrued liabilities and other	(766)	4,994
Net cash used in operating activities	(30,662)	(31,627)
Cash flows from investing activities
Maturities of marketable securities	104,716	159,800
Sales of marketable securities	14,095	0
Purchases of marketable securities	(179,166)	(143,864)
Purchases of property and equipment	(2,561)	(2,445)
Net cash (used in) provided by investing activities	(62,916)	13,491
Cash flows from financing activities
Proceeds from follow-on public offering, net of underwriting discounts, commissions and offering costs	134,616	0
Proceeds from debt financing	45,297	0
Principal repayments of debt financing	(45,297)	0
Payments of debt issuance costs	(750)	0
Payments of prepayment penalty and lender fees	(843)	0
Proceeds from the exercise of common stock options	1,463	1,490
Proceeds from issuance of common stock under employee stock purchase plan	1,915	2,203
Repurchase of unvested early exercised stock options	0	(38)
Payments of initial public offering costs	0	(167)
Net cash provided by financing activities	136,401	3,488
Effect of exchange rate changes on cash and cash equivalents	323	(37)
Net increase (decrease) in cash and cash equivalents	43,146	(14,685)
Cash and cash equivalents at
Beginning of year	10,435	25,120
End of year	53,581	10,435
Supplemental disclosure of cash flow information
Cash paid for interest	4,276	4,949
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	71	197
Unpaid purchases of property and equipment	$ 26	$ 375