Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (58,179)	$ (56,759)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	627	312
Purchase net (premium) discount on marketable securities	(102)	498
Net accretion of discount on marketable securities	(47)	(749)
Stock-based compensation	4,644	3,692
Non-cash operating lease expense	465	337
Other	(15)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,968)	(1,700)
Accounts payable	(539)	1,834
Operating lease liabilities	92	(165)
Accrued and other liabilities	(3,621)	3,302
Net cash used in operating activities	(58,643)	(49,398)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(3,280)	(318)
Purchases of marketable securities	(98,000)	(87,676)
Proceeds from maturities of marketable securities	65,056	75,929
Net cash used in investing activities	(36,224)	(12,065)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock and pre-funded warrants in public offering, net of offering costs	129,103	64,239
Proceeds from employee stock plan purchases and stock option exercises	744	826
Principal payments on finance lease obligation	(14)	(18)
Net cash provided by financing activities	129,833	65,047
Effect of exchange rate on cash, cash equivalents, and restricted cash	4
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	34,970	3,584
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	20,753	22,461
End of period	55,723	26,045
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Leased assets obtained in exchange for lease obligations	172	5,294
Unpaid amounts related to purchase of property and equipment	$ 515	$ 26