Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities
Net loss	$ (26,338)	$ (16,406)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	3,933	2,329
Vesting of common stock warrants	22	22
Change in fair value of derivative liability	7	92
Depreciation and amortization	406	383
Amortization of right-of-use assets	376	365
Net amortization (accretion) of premium (discount) on marketable securities	582	0
Changes in operating assets and liabilities
Accounts receivable	47	521
Prepaid expenses and other current assets	1,017	773
Accounts payable	(1,680)	(601)
Accrued and other liabilities	(1,074)	(1,450)
Deferred revenue	(1,219)	(1,035)
Operating lease liabilities	371	(365)
Net cash used in operating activities	(23,550)	(15,372)
Cash flows from investing activities
Purchase of marketable securities	(59,694)	0
Maturities of marketable securities	11,997	0
Acquisition of property and equipment	(6,413)	(642)
Net cash used in investing activities	(54,110)	(642)
Cash flows from financing activities
Payment of offering costs	(246)	(946)
Issuance of common stock upon exercise of stock options and warrants	875	99
Net cash provided by (used in) financing activities	629	(847)
Net decrease in cash and cash equivalents	(77,031)	(16,861)
Cash and cash equivalents, beginning of period	153,001	276,726
Cash and cash equivalents, end of period	75,970	259,865
Supplemental disclosures of noncash investing and financing information
Decrease in right-of-use assets due to reduction in operating lease liabilities upon modification	0	(478)
Unpaid offering costs	178	0
Purchases of property and equipment in accounts payable and accrued and other liabilities	$ 257	$ 145