Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (17,460)	$ (13,169)
Reconciliation of net loss to net cash used in operating activities:
Non-cash items	733	889
Changes in assets and liabilities:
Prepaid expenses and other current assets	994	456
Other assets	85	(25)
Right-of-use asset-operating	134	(9)
Accounts payable	(26)	(160)
Accrued expenses	1,085	(256)
Other liabilities		(51)
Net cash used in operating activities	(14,455)	(12,325)
Investing activities
Purchases of short-term investments	(42,777)	(88,506)
Sales and maturities of short-term investments	67,110	74,277
Purchases of property and equipment	(23)
Net cash provided by (used in) investing activities	24,310	(14,229)
Financing activities
Proceeds from public offerings, net of issuance costs	24,559	18,505
Proceeds from at-the-market offering, net of issuance costs	7,330	2,315
Proceeds from exercise of common stock warrants		55
Net cash provided by financing activities	31,889	20,875
Net increase (decrease) in cash, cash equivalents and restricted cash	41,744	(5,679)
Cash, cash equivalents and restricted cash, beginning of period	10,376	15,407
Cash, cash equivalents and restricted cash, end of period	$ 52,120	9,728
Non-cash financing activities:
At-the-market offering issuance costs included in current liabilities		$ 141