Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive loss	Total
Balance at Dec. 31, 2017	$ 2	$ 183,224	$ (171,434)		$ 11,792
Balance (in shares) at Dec. 31, 2017	2,364,526
Increase (Decrease) in Shareholders' Equity
Issuance of common stock and warrants in public offering, net of issuance costs	$ 4	38,882			38,886
Issuance of common stock and warrants in public offering, net of issuance costs (in shares)	4,200,000
Issuance of common stock for at-the-market offerings	$ 1	8,362			8,363
Issuance of common stock for at-the-market offerings (in shares)	577,195
Proceeds from exercises of common stock options		4			4
Proceeds from exercises of common stock options (in shares)	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
Increase (Decrease) in Shareholders' Equity
Issuance of common stock and warrants in public offering, net of issuance costs	$ 4	18,501			$ 18,505
Issuance of common stock and warrants in public offering, net of issuance costs (in shares)	4,000,000
Issuance of common stock for at-the-market offerings	$ 1	6,995			6,996
Issuance of common stock for at-the-market offerings (in shares)	1,282,904
Proceeds from exercises of common stock options		54			$ 54
Proceeds from exercises of common stock options (in shares)	8,700				0
Stock-based compensation expense		1,512			$ 1,512
Unrealized losses on short-term investments				$ 4	4
Net loss			(26,293)		(26,293)
Balance at Dec. 31, 2019	$ 12	$ 259,305	$ (223,597)		$ 35,720
Balance (in shares) at Dec. 31, 2019	12,433,600				12,433,600