Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (40,146)	$ (35,186)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	376	207
Purchase net discount on marketable securities	19	480
Net accretion of discount on marketable securities	(58)	(543)
Stock-based compensation	2,948	2,326
Non-cash operating lease expense	306	191
Other	(15)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,637)	(2,223)
Accounts payable	1,318	2,141
Operating lease liabilities	(277)	(178)
Accrued and other liabilities	(3,941)	595
Net cash used in operating activities	(41,107)	(32,190)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(2,714)	(175)
Purchases of marketable securities	(75,500)	(77,956)
Proceeds from maturities of marketable securities	36,206	50,054
Net cash used in investing activities	(42,008)	(28,077)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock and pre-funded warrants in public offering, net of offering costs	129,250	64,298
Proceeds from employee stock plan purchases and stock option exercises	333	450
Principal payments on finance lease obligation	(8)	(12)
Net cash provided by financing activities	129,575	64,736
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	46,460	4,469
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	20,753	22,461
End of period	67,213	26,930
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Leased assets obtained in exchange for lease obligations	176	$ 5,294
Unpaid amounts related to purchase of property and equipment	$ 440