CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Treasury Stock	Warrants	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2016		12,000	31,595,000	0
Beginning balance at Dec. 31, 2016	$ 24,708	$ 38,389	$ 329,720	$ 0	$ 190	$ 0	$ (343,591)
Increase (Decrease) in Shareholders' Equity
Net loss	(17,286)						(17,286)
Conversion of Series B-1 or B-2 preferred stock for common stock (in shares)		(12,000)	1,094,000
Conversion of Series B-1 or B-2 preferred stock for common stock	0	$ (38,389)	$ 38,389
Compensation expense related to stock options granted, net of forfeitures	2,680		$ 2,680
Issuance of common stock, net of issuance costs (in shares)			1,983,000
Issuance of common stock, net of issuance costs	7,188		$ 7,188
Stock option exercises (in shares)			199,000
Stock option exercises	608		$ 608
Shares issued under the Employee Stock Purchase Plan (in shares)			173,000
Shares issued under the Employee Stock Purchase Plan	425		$ 425
Issuance of warrants	207				207
Exercise of warrants resulting in issuance of common stock (Note 11) (in shares)			817,000
Exercise of warrants resulting in issuance of common stock	4,010		$ 4,010
Net change in unrealized (gain) loss on investments	0
Ending balance (in shares) at Dec. 31, 2017		0	35,861,000	0
Ending balance at Dec. 31, 2017	22,540	$ 0	$ 383,020	$ 0	397	0	(360,877)
Increase (Decrease) in Shareholders' Equity
Net loss	(8,137)						(8,137)
Compensation expense related to stock options granted, net of forfeitures	7,223		$ 7,223
Issuance of common stock, net of issuance costs (in shares)			5,750,000
Issuance of common stock, net of issuance costs	70,028		$ 70,028
Stock option exercises (in shares)			1,180,000
Stock option exercises	3,705		$ 3,705
Shares issued under the Employee Stock Purchase Plan (in shares)			106,000
Shares issued under the Employee Stock Purchase Plan	656		$ 656
Exercise of warrants resulting in issuance of common stock (Note 11) (in shares)			681,000
Exercise of warrants resulting in issuance of common stock	6,255		$ 6,548		(293)
Net change in unrealized (gain) loss on investments	(39)					(39)
Ending balance (in shares) at Dec. 31, 2018		0	43,578,000	0
Ending balance at Dec. 31, 2018	102,231	$ 0	$ 471,180	$ 0	104	(39)	(369,014)
Increase (Decrease) in Shareholders' Equity
Net loss	(9,665)						(9,665)
Compensation expense related to stock options granted, net of forfeitures	$ 13,179		$ 13,179
Stock option exercises (in shares)	1,197,016		1,197,000
Stock option exercises	$ 4,354		$ 4,354
Shares issued under the Employee Stock Purchase Plan (in shares)			69,000
Shares issued under the Employee Stock Purchase Plan	932		$ 932
Exercise of warrants resulting in issuance of common stock (Note 11) (in shares)			20,000
Exercise of warrants resulting in issuance of common stock	0		$ 104		(104)
Net change in unrealized (gain) loss on investments	60					60
Ending balance (in shares) at Dec. 31, 2019		0	44,864,000
Ending balance at Dec. 31, 2019	$ 111,091		$ 489,749		$ 0	$ 21	$ (378,679)