Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (9,467)	$ (12,148)	$ (36,765)	$ (37,658)
Change in unrealized gain (loss) on short-term investments	25	(28)	39	(43)
Comprehensive loss	$ (9,442)	$ (12,176)	$ (36,726)	$ (37,701)