CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net loss	$ (12,242)	$ (12,772)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	4,030	2,622
Depreciation and amortization	340	249
Bad debt expense	0	192
Accretion on marketable securities	331	(25)
Amortization of debt issuance costs	88	65
Loss on sale and disposal of property and equipment	104	0
Changes in operating assets and liabilities:
Accounts receivable	581	2,207
Inventory	(1,725)	(256)
Prepaid expenses and other assets	20	581
Accounts payable	1,059	76
Accrued liabilities and other	(1,945)	(2,294)
Net cash used in operating activities	(9,359)	(9,355)
Cash flows from investing activities
Maturities of marketable securities	33,200	21,000
Purchases of marketable securities	(38,346)	(16,777)
Purchases of property and equipment	(1,976)	(884)
Net cash (used in) provided by investing activities	(7,122)	3,339
Cash flows from financing activities
Proceeds from follow-on public offering, net of underwriting discounts, commissions and offering costs	0	62,978
Proceeds from the exercise of stock options	601	174
Net cash provided by financing activities	601	63,152
Effect of exchange rate changes on cash and cash equivalents	(337)	(3)
Net (decrease) increase in cash and cash equivalents	(16,217)	57,133
Cash and cash equivalents at
Beginning of period	53,581	10,435
End of period	37,364	67,568
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	9	27
Unpaid purchases of property and equipment	$ 1,195	$ 52