Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (65,801)	$ (80,893)	$ (78,254)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,576	996	418
Purchase net (premium) discount on marketable securities	(344)	(286)	504
Net amortization of premium (accretion of discount) on marketable securities	548	73	(818)
Stock-based compensation	8,038	6,256	4,876
Non-cash operating lease expense	425	628	483
Other	9	(9)	(5)
Changes in operating assets and liabilities:
License and development receivable	(815)	0	0
Prepaid expenses and other assets	(1,216)	(1,101)	(346)
Accounts payable	1,065	(544)	2,583
Operating lease liabilities	(404)	251	(258)
Deferred revenue	3,576	0	0
Accrued and other liabilities	(373)	(1,146)	5,125
Net cash used in operating activities	(53,716)	(75,775)	(65,692)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(573)	(4,280)	(1,492)
Purchases of marketable securities	(133,079)	(129,000)	(91,926)
Proceeds from maturities and sales of marketable securities	111,033	125,676	91,679
Net cash used in investing activities	(22,619)	(7,604)	(1,739)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock and pre-funded warrants in public and at-the-market offerings, net of offering costs	0	153,716	64,298
Proceeds from employee stock plan purchases and stock option exercises	1,903	816	1,450
Principal payments on finance lease obligation	(510)	(20)	(25)
Net cash provided by financing activities	1,393	154,512	65,723
Effect of exchange rate on cash, cash equivalents, and restricted cash	(15)	51	0
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(74,957)	71,184	(1,708)
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	91,937	20,753	22,461
End of period	16,980	91,937	20,753
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Leased assets obtained in exchange for lease obligations	872	172	5,294
Unpaid amounts related to purchase of property and equipment	$ 0	$ 224	$ 356