Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Operating activities
Net loss	$ (16,289)	$ (31,039)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,522	4,758
Depreciation and amortization	406	870
Impairment of property and equipment	3,418	0
Amortization of operating lease right-of-use assets	580	509
Amortization and accretion of premiums/discounts on available-for-sale securities	(1,178)	3
Gain on sale of property and equipment	(47)	0
Changes in operating assets and liabilities:
Other current assets and other non-current assets	1,046	(537)
Accounts payable and accrued liabilities	(5,876)	614
Operating lease liabilities	(664)	(563)
Net cash used in operating activities	(17,082)	(25,385)
Investing activities
Purchases of property and equipment	(551)	(684)
Proceeds from sale of property and equipment	2,115	0
Purchases of available-for-sale securities	(55,269)	(39,067)
Proceeds from maturities of available-for-sale securities	64,000	0
Net cash provided by (used in) investing activities	10,295	(39,751)
Financing activities
Proceeds from exercise of stock options	0	134
Payment on finance lease obligations	(364)	(2)
Proceeds from the issuance of common stock under Employee Stock Purchase Plan	4	63
Net cash provided by (used in) financing activities	(360)	195
Net change in cash, cash equivalents, and restricted cash during the period	(7,147)	(64,941)
Cash, cash equivalents, and restricted cash, beginning of period	38,765	143,345
Cash, cash equivalents, and restricted cash, end of period	31,618	78,404
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment unpaid at period-end	$ 0	$ 265