Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (11,227)	$ (8,003)
Unrealized (losses) gains on investments, net of tax	(20)	34
Comprehensive loss	$ (11,247)	$ (7,969)