Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net loss	$ (45,581)	$ (50,038)	$ (29,281)
Other comprehensive income (loss):
Unrealized gain (loss) on short-term investments	14	(65)	22
Comprehensive loss	$ (45,567)	$ (50,103)	$ (29,259)