Condensed 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, 2018	$ 7	$ 232,243	$ (197,304)	$ (4)
Balance (in shares) at Dec. 31, 2018	7,141,996
Increase (Decrease) in Shareholders' Equity
Issuance of common stock for at-the-market offerings	$ 1	2,173
Issuance of common stock for at-the-market offerings (in shares)	403,241
Issuance of common stock and warrants in public offerings	$ 4	18,501
Issuance of common stock and warrants in public offerings (in shares)	4,000,000
Issuance of common stock upon exercise of common stock warrants		55
Issuance of common stock upon exercise of common stock warrants (in shares)	8,700
Stock-based compensation expense		849
Realized gain on short-term investments				5	$ 5
Net loss			(13,169)		(13,169)
Balance at Jun. 30, 2019	$ 12	253,821	(210,473)	1	43,361
Balance (in shares) at Jun. 30, 2019	11,553,937
Balance at Mar. 31, 2019	$ 11	253,200	(203,342)
Balance (in shares) at Mar. 31, 2019	11,496,242
Increase (Decrease) in Shareholders' Equity
Issuance of common stock for at-the-market offerings	$ 1	128
Issuance of common stock for at-the-market offerings (in shares)	49,495
Issuance of common stock upon exercise of common stock warrants		52
Issuance of common stock upon exercise of common stock warrants (in shares)	8,200
Stock-based compensation expense		441
Realized gain on short-term investments				1	1
Net loss			(7,131)		(7,131)
Balance at Jun. 30, 2019	$ 12	253,821	(210,473)	1	43,361
Balance (in shares) at Jun. 30, 2019	11,553,937
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
Increase (Decrease) in Shareholders' Equity
Issuance of common stock for at-the-market offerings	$ 2	7,328
Issuance of common stock for at-the-market offerings (in shares)	1,100,001
Issuance of common stock and warrants in public offerings	$ 5	24,554
Issuance of common stock and warrants in public offerings (in shares)	5,290,000
Stock-based compensation expense		710
Realized gain on short-term investments				1	$ 1
Net loss			(17,460)		(17,460)
Balance at Jun. 30, 2020	$ 19	291,897	(241,057)	1	$ 50,860
Balance (in shares) at Jun. 30, 2020	18,823,601				18,823,601
Balance at Mar. 31, 2020	$ 18	285,257	(231,549)	(15)
Balance (in shares) at Mar. 31, 2020	17,897,172
Increase (Decrease) in Shareholders' Equity
Issuance of common stock for at-the-market offerings	$ 1	6,269
Issuance of common stock for at-the-market offerings (in shares)	926,429
Stock-based compensation expense		371
Realized gain on short-term investments				16	$ 16
Net loss			(9,508)		(9,508)
Balance at Jun. 30, 2020	$ 19	$ 291,897	$ (241,057)	$ 1	$ 50,860
Balance (in shares) at Jun. 30, 2020	18,823,601				18,823,601