STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)	ACCUMULATED DEFICIT	Total
Balance at Dec. 31, 2012	$ 624	$ 500,655	$ 102	$ (420,352)	$ 81,029
Balance (in shares) at Dec. 31, 2012	62,399,827
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises and issuance of stock	$ 2	72			74
Stock option exercises and issuance of stock (in shares)	200,395
Employee stock purchase plan	$ 1	279			280
Employee stock purchase plan (in shares)	135,985
Stock based compensation expense		3,878			3,878
Change in unrealized gain (loss) on marketable securities			(35)		(35)
Net loss				(24,600)	(24,600)
Balance at Dec. 31, 2013	$ 627	504,884	67	(444,952)	60,626
Balance (in shares) at Dec. 31, 2013	62,736,207
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted shares issued net of forfeitures and shares redeemed for taxes
Restricted shares issued net of forfeitures and shares redeemed for taxes (in shares)	(5,257)
Employee stock purchase plan	$ 1	104			105
Employee stock purchase plan (in shares)	90,831
Stock based compensation expense		3,282			3,282
Change in unrealized gain (loss) on marketable securities			(77)		(77)
Net loss				(23,391)	(23,391)
Balance at Dec. 31, 2014	$ 628	508,270	(10)	(468,343)	$ 40,545
Balance (in shares) at Dec. 31, 2014	62,821,781				62,821,781
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted shares issued net of forfeitures and shares redeemed for taxes
Restricted shares issued net of forfeitures and shares redeemed for taxes (in shares)	13,242
Employee stock purchase plan	$ 1	133			$ 134
Employee stock purchase plan (in shares)	104,757
Stock based compensation expense		2,261			2,261
Change in unrealized gain (loss) on marketable securities			13		13
Net loss				(13,774)	(13,774)
Balance at Dec. 31, 2015	$ 629	$ 510,664	$ 3	$ (482,117)	$ 29,179
Balance (in shares) at Dec. 31, 2015	62,939,780				62,939,780