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, 2017	$ 2	$ 183,224	$ (171,434)
Balance (in shares) at Dec. 31, 2017	2,364,526
Increase (Decrease) in Shareholders' Equity
Issuance of common stock for at-the-market offerings	$ 1	8,312
Issuance of common stock for at-the-market offerings (in shares)	539,026
Issuance of common stock and warrants in public offerings	$ 4	38,881
Issuance of common stock and warrants in public offerings (in shares)	4,200,000
Issuance of common stock upon exercise of common stock options and warrants		4
Issuance of common stock upon exercise of common stock options and warrants (in shares)	291
Stock-based compensation expense		1,340
Realized gain on short-term investments				$ (5)	$ (5)
Net loss			(19,810)		(19,810)
Balance at Sep. 30, 2018	$ 7	231,761	(191,244)	(5)	40,519
Balance (in shares) at Sep. 30, 2018	7,103,843
Balance at Jun. 30, 2018	$ 7	231,371	(185,565)
Balance (in shares) at Jun. 30, 2018	7,103,843
Increase (Decrease) in Shareholders' Equity
Issuance of common stock and warrants in public offerings		(26)
Stock-based compensation expense		416
Realized gain on short-term investments				(5)	(5)
Net loss			(5,679)		(5,679)
Balance at Sep. 30, 2018	$ 7	231,761	(191,244)	(5)	40,519
Balance (in shares) at Sep. 30, 2018	7,103,843
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 for at-the-market offerings	$ 1	3,223
Issuance of common stock for 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 options and warrants		54
Issuance of common stock upon exercise of common stock options and warrants (in shares)	8,700
Stock-based compensation expense		1,227
Realized 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				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 for at-the-market offerings		1,049
Issuance of common stock for at-the-market offerings (in shares)	161,349
Stock-based compensation expense		378
Realized 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				11,715,286