CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands	Total	Preferred Stock	Common Stock	Treasury Stock	Warrants	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2015		13	23,789	(1,250)
Beginning balance at Dec. 31, 2015	$ 22,130,000	$ 41,539,000	$ 307,766,000	$ (3,150,000)	$ 0	$ 0	$ (324,025,000)
Increase (Decrease) in Shareholders' Equity
Net loss	(19,566,000)						(19,566,000)
Conversion of preferred stock for common stock (Note 9) (in shares)		(1)		1,250
Conversion of preferred stock for common stock (Note 9)	0	$ (3,150,000)		$ 3,150,000
Compensation expense related to stock options granted, net of forfeitures	2,499,000		$ 2,499,000
Issuance of common stock, net of issuance costs (in shares)			7,538
Issuance of common stock, net of issuance costs	18,868,000		$ 18,868,000
Stock option exercises (in shares)			39
Stock option exercises	120,000		$ 120,000
Shares issued under the Employee Stock Purchase Plan (in shares)			229
Shares issued under the Employee Stock Purchase Plan	467,000		$ 467,000
Issuance of warrants	190,000				190,000
Ending balance (in shares) at Dec. 31, 2016		12	31,595	0
Ending balance at Dec. 31, 2016	24,708,000	$ 38,389,000	$ 329,720,000	$ 0	190,000	0	(343,591,000)
Increase (Decrease) in Shareholders' Equity
Net loss	(17,286,000)						(17,286,000)
Conversion of preferred stock for common stock (Note 9) (in shares)		(12)	1,094
Conversion of preferred stock for common stock (Note 9)	0	$ (38,389,000)	$ 38,389,000
Compensation expense related to stock options granted, net of forfeitures	2,680,000		$ 2,680,000
Issuance of common stock, net of issuance costs (in shares)			1,983
Issuance of common stock, net of issuance costs	7,188,000		$ 7,188,000
Stock option exercises (in shares)			199
Stock option exercises	608,000		$ 608,000
Shares issued under the Employee Stock Purchase Plan (in shares)			173
Shares issued under the Employee Stock Purchase Plan	425,000		$ 425,000
Issuance of warrants	207,000				207,000
Exercise of warrants resulting in the issuance of common stock (Note 11) (in shares)			817
Exercise of warrants resulting in the issuance of common stock	4,010,000		$ 4,010,000
Ending balance (in shares) at Dec. 31, 2017		0	35,861	0
Ending balance at Dec. 31, 2017	22,540,000	$ 0	$ 383,020,000	$ 0	397,000	0	(360,877,000)
Increase (Decrease) in Shareholders' Equity
Net loss	(8,137,000)						(8,137,000)
Compensation expense related to stock options granted, net of forfeitures	7,223,000		$ 7,223,000
Issuance of common stock, net of issuance costs (in shares)			5,750
Issuance of common stock, net of issuance costs	70,028,000		$ 70,028,000
Stock option exercises (in shares)			1,180
Stock option exercises	3,705,000		$ 3,705,000
Shares issued under the Employee Stock Purchase Plan (in shares)			106
Shares issued under the Employee Stock Purchase Plan	656,000		$ 656,000
Exercise of warrants resulting in the issuance of common stock (Note 11) (in shares)			681
Exercise of warrants resulting in the issuance of common stock	6,255,000		$ 6,548,000		(293,000)
Net change in unrealized loss on investments	(39,000)					(39)
Ending balance (in shares) at Dec. 31, 2018		0	43,578	0
Ending balance at Dec. 31, 2018	$ 102,231,000	$ 0	$ 471,180,000	$ 0	$ 104,000	$ (39,000)	$ (369,014,000)