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 in at-the-market offerings	$ 1	3,223
Issuance of common stock in at-the-market offerings (in shares)	564,590
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		54
Issuance of common stock upon exercise of common stock warrants (in shares)	8,700
Stock-based compensation expense		1,227
Realized (loss) gain on short-term investments				4	$ 4
Net loss			(19,683)		(19,683)
Balance at Sep. 30, 2019	$ 12	255,248	(216,987)		38,273
Balance (in shares) at Sep. 30, 2019	11,715,286
Balance at Jun. 30, 2019	$ 12	253,821	(210,473)	1
Balance (in shares) at Jun. 30, 2019	11,553,937
Increase (Decrease) in Shareholders' Equity
Issuance of common stock in at-the-market offerings		1,049
Issuance of common stock in at-the-market offerings (in shares)	161,349
Stock-based compensation expense		378
Realized (loss) gain on short-term investments				(1)	(1)
Net loss			(6,514)		(6,514)
Balance at Sep. 30, 2019	$ 12	255,248	(216,987)		38,273
Balance (in shares) at Sep. 30, 2019	11,715,286
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 in at-the-market offerings	$ 3	16,267
Issuance of common stock in at-the-market offerings (in shares)	2,353,737
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		1,084
Net loss			(28,322)		$ (28,322)
Balance at Sep. 30, 2020	$ 20	301,210	(251,919)		$ 49,311
Balance (in shares) at Sep. 30, 2020	20,077,337				20,077,337
Balance at Jun. 30, 2020	$ 19	291,897	(241,057)	1
Balance (in shares) at Jun. 30, 2020	18,823,601
Increase (Decrease) in Shareholders' Equity
Issuance of common stock in at-the-market offerings	$ 1	8,938
Issuance of common stock in at-the-market offerings (in shares)	1,253,736
Stock-based compensation expense		375
Realized (loss) gain on short-term investments				$ (1)	$ (1)
Net loss			(10,862)		(10,862)
Balance at Sep. 30, 2020	$ 20	$ 301,210	$ (251,919)		$ 49,311
Balance (in shares) at Sep. 30, 2020	20,077,337				20,077,337