Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (16,632)	$ (16,494)
Change in unrealized gain (loss) on available-for-sale securities, net of tax	(112)	83
Comprehensive loss	$ (16,744)	$ (16,411)