Consolidated Statements of Comprehensive Loss (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (12,317)	$ (10,212)	$ (40,646)	$ (40,856)
Other comprehensive gain (loss):
Unrealized loss on marketable securities	(9)		(9)	(1)
Comprehensive loss	$ (12,326)	$ (10,212)	$ (40,655)	$ (40,857)