Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (25,048)	$ (40,146)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	753	376
Purchase net (premium) discount on marketable securities	(405)	19
Net amortization of premium (accretion of discount) on marketable securities	341	(58)
Stock-based compensation	3,837	2,948
Non-cash operating lease expense	219	306
Other	4	(15)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,876)	(1,637)
Accounts payable	(55)	1,318
Operating lease liabilities	(155)	(277)
Deferred revenue	7,804
Accrued and other liabilities	(1,867)	(3,941)
Net cash used in operating activities	(17,448)	(41,107)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(480)	(2,714)
Purchases of marketable securities	(93,579)	(75,500)
Proceeds from maturities of marketable securities	56,000	36,206
Net cash used in investing activities	(38,059)	(42,008)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock and pre-funded warrants in public offering, net of offering costs		129,250
Proceeds from employee stock plan purchases and stock option exercises	403	333
Principal payments on finance lease obligation	(233)	(8)
Net cash provided by financing activities	170	129,575
Effect of exchange rate on cash, cash equivalents, and restricted cash	11
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(55,326)	46,460
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	91,937	20,753
End of period	36,611	67,213
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Leased assets obtained in exchange for lease obligations	872	176
Unpaid amounts related to purchase of property and equipment	$ 23	$ 440