Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Gain	Total
Balance at Dec. 31, 2016	$ 2	$ 173,158	$ (144,070)	$ (4)	$ 29,086
Balance (in shares) at Dec. 31, 2016	1,881,758
Increase (Decrease) in Stockholders' Equity
Issuance of common stock for at-the-market offerings, net of issuance costs of $0.4 million and $0.6 million for the years 2018 and 2017 respectively		8,036			8,036
Issuance of common stock for at-the-market offerings, net of issuance costs of $0.4 million and $0.6 million for the years 2018 and 2017 respectively (in shares)	480,480
Proceeds from exercises of common stock options		23			23
Proceeds from exercises of common stock options (in shares)	2,288
Stock-based compensation expense		2,007			2,007
Unrealized losses on short-term investments					4
Realized gain on short-term investments				4	4
Net loss			(27,364)		(27,364)
Balance at Dec. 31, 2017	$ 2	183,224	(171,434)		$ 11,792
Balance (in shares) at Dec. 31, 2017	2,364,526				2,364,526
Increase (Decrease) in Stockholders' Equity
Issuance of common stock and warrants in public offerings, net of $3.1 million in issuance costs	$ 4	38,882			$ 38,886
Issuance of common stock and warrants in public offerings, net of $3.1 million in issuance costs (in shares)	4,200,000
Issuance of common stock for at-the-market offerings, net of issuance costs of $0.4 million and $0.6 million for the years 2018 and 2017 respectively	$ 1	8,362			8,363
Issuance of common stock for at-the-market offerings, net of issuance costs of $0.4 million and $0.6 million for the years 2018 and 2017 respectively (in shares)	577,195
Proceeds from exercises of common stock options		4			$ 4
Proceeds from exercises of common stock options (in shares)	291				291
Stock-based compensation expense		1,771			$ 1,771
Fractional shares eliminated pursuant to reverse stock split	(16)
Unrealized losses on short-term investments				(4)	(4)
Net loss			(25,870)		(25,870)
Balance at Dec. 31, 2018	$ 7	$ 232,243	$ (197,304)	$ (4)	$ 34,942
Balance (in shares) at Dec. 31, 2018	7,141,996				7,141,996