Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (45,355)	$ (58,179)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,165	627
Purchase net premium on marketable securities	(374)	(102)
Net amortization of premium (accretion of discount) on marketable securities	490	(47)
Stock-based compensation	5,944	4,644
Non-cash operating lease expense	334	465
Other	2	(15)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,555)	(1,968)
Accounts payable	(390)	(539)
Operating lease liabilities	(286)	92
Deferred revenue	6,405
Accrued and other liabilities	(828)	(3,621)
Net cash used in operating activities	(34,448)	(58,643)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(573)	(3,280)
Purchases of marketable securities	(119,829)	(98,000)
Proceeds from maturities of marketable securities	88,120	65,056
Net cash used in investing activities	(32,282)	(36,224)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock and pre-funded warrants in public offering, net of offering costs		129,103
Proceeds from employee stock plan purchases and stock option exercises	1,654	744
Principal payments on finance lease obligation	(341)	(14)
Net cash provided by financing activities	1,313	129,833
Effect of exchange rate on cash, cash equivalents, and restricted cash	(18)	4
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(65,435)	34,970
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	91,937	20,753
End of period	26,502	55,723
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Leased assets obtained in exchange for lease obligations	$ 872	172
Unpaid amounts related to purchase of property and equipment		$ 515