Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net loss	$ (19,683)	$ (19,810)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	23	111
Stock-based compensation expense	1,227	1,340
Accretion of discount/premium on investment securities	9	(4)
Non-cash interest expense		38
Gain on disposal of property and equipment		(297)
Services received in non-monetary exchange	18	8
Changes in assets and liabilities:
Prepaid expenses and other current assets	(671)	(120)
Other assets	(25)
Right-of-use asset-operating	(36)
Accounts payable	682	274
Accrued expenses	(287)	267
Other liabilities	(56)	(3)
Net cash used in operating activities	(18,799)	(18,196)
Investing activities
Purchases of short-term investments	(123,355)	(39,364)
Sales and maturities of short-term investments	122,777	16,000
Proceeds from sale of property and equipment		365
Net cash used in investing activities	(578)	(22,999)
Financing activities
Proceeds from public offerings, net of issuance costs	18,505	38,885
Proceeds from at-the-market offering, net of issuance costs	3,289	8,313
Proceeds from exercise of common stock options and warrants	54	4
Payments on borrowing		(2,500)
Net cash provided by financing activities	21,848	44,702
Net increase in cash, cash equivalents and restricted cash	2,471	3,507
Cash, cash equivalents and restricted cash, beginning of period	15,407	16,482
Cash, cash equivalents and restricted cash, end of period	17,878	19,989
Supplemental disclosure of cash flow information
Cash paid for interest		$ 79
Non-cash financing activities
At-the-market issuance costs included in current liabilities	$ 65