Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (7,952)	$ (6,038)
Reconciliation of net loss to net cash used in operating activities:
Non-cash items	341	416
Accretion of discount/premium on investment securities	2	7
Services received in non-monetary exchange	8	6
Changes in assets and liabilities:
Prepaid expenses and other current assets	669	354
Other assets		(25)
Right-of-use asset-operating	51	12
Accounts payable	(501)	48
Accrued expenses	393	(1,313)
Other liabilities		(54)
Net cash used in operating activities	(6,989)	(6,587)
Investing activities
Purchases of short-term investments	(42,777)	(47,015)
Sales and maturities of short-term investments	27,345	29,277
Net cash used in investing activities	(15,432)	(17,738)
Financing activities
Proceeds from public offerings, net of issuance costs	24,564	18,635
Proceeds from at-the-market offering, net of issuance costs	1,060	2,045
Proceeds from exercise of common stock options and warrants		3
Net cash provided by financing activities	25,624	20,683
Net increase (decrease) in cash, cash equivalents and restricted cash	3,203	(3,642)
Cash, cash equivalents and restricted cash, beginning of period	10,376	15,407
Cash, cash equivalents and restricted cash, end of period	13,579	11,765
Non-cash investing activities:
Fixed asset purchases included in accounts payable	9
Non-cash financing activities
Public offering issuance costs included in current liabilities	$ 5	$ 130