Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Operating activities
Net loss	$ (20,815)	$ (44,112)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,694	6,789
Depreciation and amortization	483	1,193
Impairment of property and equipment	3,418	0
Impairment of operating lease right-of-use asset	146	0
Amortization of operating lease right-of-use assets	884	776
Amortization and accretion of premiums/discounts on available-for-sale securities	(1,880)	(105)
Loss (gain) on sale of property and equipment	(47)	108
Changes in operating assets and liabilities:
Other current assets and other non-current assets	1,384	(287)
Accounts payable and accrued liabilities	(5,605)	1,823
Operating lease liabilities	(1,013)	(859)
Net cash used in operating activities	(21,351)	(34,674)
Investing activities
Purchases of property and equipment	(551)	(1,006)
Proceeds from sale of property and equipment	2,115	0
Purchases of available-for-sale securities	(91,883)	(81,595)
Proceeds from maturities of available-for-sale securities	99,000	15,000
Net cash provided by (used in) investing activities	8,681	(67,601)
Financing activities
Proceeds from exercise of stock options	0	134
Payment on finance lease obligations	(365)	(54)
Proceeds from the issuance of common stock under Employee Stock Purchase Plan	4	63
Net cash provided by (used in) financing activities	(361)	143
Net change in cash, cash equivalents, and restricted cash during the period	(13,031)	(102,132)
Cash, cash equivalents, and restricted cash, beginning of period	38,765	143,345
Cash, cash equivalents, and restricted cash, end of period	25,734	41,213
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment unpaid at period-end	$ 0	$ 28