Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Convertible Preferred Stock [Member]
Beginning balance at Dec. 31, 2017	$ 64,245	$ 30	$ 328,519	$ (120)	$ (264,186)	$ 2
Begining balance, Shares at Dec. 31, 2017		29,789,162				2,285,952
Issuance of common stock upon exercise of options and release of restricted stock units	8		8
Issuance of common stock upon exercise of options and release of restricted stock units, Share		39,561
Stock-based compensation	928		928
Net unrealized gain on investments, net of tax	(16)			(16)
Net loss	(10,667)				(10,667)
Ending balance at Mar. 31, 2018	54,498	$ 30	329,455	(136)	(274,853)	$ 2
Ending balance, Shares at Mar. 31, 2018		29,828,723				2,285,952
Beginning balance at Dec. 31, 2018	33,650	$ 31	332,378	(60)	(298,701)	$ 2
Begining balance, Shares at Dec. 31, 2018		30,579,076				2,285,952
Conversion of preferred stock to common stock		$ 3	(3)
Conversion of preferred stock to common stock, shares		3,209,955				(641,991)
Issuance of common stock from at the market offerings, net of offering costs	1,381	$ 3	1,378
Issuance of common stock from at the market offerings, net of offering costs, Shares		2,711,158
Stock-based compensation	571		571
Net unrealized gain on investments, net of tax	20			20
Net loss	(6,137)				(6,137)
Ending balance at Mar. 31, 2019	$ 29,485	$ 37	$ 334,324	$ (40)	$ (304,838)	$ 2
Ending balance, Shares at Mar. 31, 2019		36,500,189				1,643,961