Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (35,118)	$ (30,608)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	723	563
Stock-based compensation expense	10,628	4,953
Amortization of premiums on investments, net	451	145
Amortization of debt discount and debt issuance costs	119	35
Amortization of right-of-use asset	627	447
Non-cash interest expense	193	249
Loss on disposal of property and equipment		51
Change in provision for doubtful accounts receivable		(26)
Provision for excess and obsolete inventories	56	109
Changes in assets and liabilities:
Accounts receivable	(1,906)	(771)
Inventories	(3,744)	(732)
Prepaid expenses and other current assets	(2,014)	(565)
Other assets	(107)	200
Accounts payable	1,304	29
Accrued liabilities	629	(2,054)
Other liabilities	656	176
Net cash used in operating activities	(27,503)	(27,799)
Cash flows from investing activities
Purchases of property and equipment	(2,006)	(587)
Purchases of investments		(58,884)
Proceeds from maturity of investments	60,400	37,180
Net cash provided by (used in) investing activities	58,394	(22,291)
Cash flows from financing activities
Proceeds from public offerings, net of underwriting discount, commissions and offering costs paid		70,568
Proceeds from issuance of common stock	5,207	2,809
Net cash provided by financing activities	5,207	73,377
Net change in cash, cash equivalents and restricted cash	36,098	23,287
Cash, cash equivalents and restricted cash, beginning of period	69,776	39,491
Cash, cash equivalents and restricted cash, end of period	105,874	62,778
Supplemental disclosure of cash flow information
Cash paid for interest	1,571	3,336
Noncash investing and financing activities:
Accounts payable and accrued liabilities for purchases of property and equipment	1,298	118
Offering costs in accrued liabilities		$ 25
Right-of-use asset obtained in exchange for lease obligation	$ 3,398