Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated deficit [Member]
Beginning balance at Dec. 31, 2016	$ 8,761		$ 164,707	$ (155,946)
Beginning balance, shares at Dec. 31, 2016		1,485,053
Issuance of common stock, net of issuance costs	16,310		16,310
Issuance of common stock, net of issuance costs, shares		605,336
Exercise of common stock options	304		304
Exercise of common stock options, shares		13,843
Vesting of restricted stock units, shares		518
Stock-based compensation	2,818		2,818
Net loss	(18,056)			(18,056)
Ending balance at Dec. 31, 2017	10,137		184,139	(174,002)
Ending balance, shares at Dec. 31, 2017		2,104,750
Issuance of common stock, net of issuance costs	$ 19,297		19,297
Issuance of common stock, net of issuance costs, shares		2,827,973
Exercise of common stock options, shares	0
Stock-based compensation	$ 2,973		2,973
Net loss	(20,563)			(20,563)
Ending balance at Dec. 31, 2018	$ 11,844		$ 206,409	$ (194,565)
Ending balance, shares at Dec. 31, 2018		4,932,723