Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Operating activities
Net loss	$ (14,204)	$ (15,351)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,191	2,446
Depreciation and amortization	329	411
Impairment of property and equipment	3,418	0
Amortization of operating lease right-of-use assets	286	250
Amortization and accretion of premiums/discounts on available-for-sale securities	(531)	0
Loss on disposal of property and equipment	190	0
Changes in operating assets and liabilities:
Other current assets and other non-current assets	552	(803)
Accounts payable and accrued liabilities	(3,938)	(769)
Operating lease liabilities	(326)	(275)
Net cash used in operating activities	(13,033)	(14,091)
Investing activities
Purchases of property and equipment	(419)	(452)
Purchases of available-for-sale securities	(28,375)	0
Proceeds from maturities of available-for-sale securities	39,500	0
Net cash provided by (used in) investing activities	10,706	(452)
Financing activities
Proceeds from exercise of stock options	0	134
Payments on finance lease obligations	(66)	(1)
Net cash provided by (used in) financing activities	(66)	133
Net change in cash, cash equivalents, and restricted cash during the period	(2,393)	(14,410)
Cash, cash equivalents, and restricted cash, beginning of period	38,765	143,345
Cash, cash equivalents, and restricted cash, end of period	36,372	128,935
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment unpaid at period-end	$ 99	$ 91