Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (26,293)	$ (25,870)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	26	119
Stock-based compensation expense	1,512	1,771
Accretion of discount/premium on investment securities	5	(6)
Non-cash interest expense		37
Gain on disposal of property and equipment	18	(297)
Services received in non-monetary exchange	33	19
Changes in assets and liabilities:
Prepaid expenses and other current assets	(1,289)	(177)
Other assets		(85)
Right-of-use asset-operating	(96)
Accounts payable	(211)	662
Accrued expenses	(205)	396
Other liabilities	(69)	(34)
Net cash used in operating activities	(26,569)	(23,465)
Investing activities
Purchases of short-term investments	(155,197)	(70,364)
Sales and maturities of short-term investments	151,127	48,090
Purchases of property and equipment	(12)
Proceeds from sale of property and equipment		369
Net cash used in investing activities	(4,082)	(21,905)
Financing activities
Proceeds from public offerings, net of issuance costs	18,505	38,886
Proceeds from at-the-market offering, net of issuance costs	7,061	8,253
Proceeds from exercise of common stock options and warrants	54	4
Payments on borrowing		(2,848)
Net cash provided by financing activities	25,620	44,295
Net increase in cash, cash equivalents and restricted cash	(5,031)	(1,075)
Cash, cash equivalents and restricted cash, beginning of period	15,407	16,482
Cash, cash equivalents and restricted cash, end of period	10,376	15,407
Supplemental disclosure of cash flow information
Cash paid for interest		79
Non-cash investing activities:
Fixed asset purchases included in accounts payable		18
Non-cash financing activities
At-the-market issuance costs included in current liabilities	$ 65	$ 110