CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - 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	$ (14,376)	$ (15,680)	$ (49,405)	$ (41,112)
Other comprehensive income (loss):
Unrealized gains (losses) on available-for-sale investments, net of taxes of $137 and ($1,700) for the three months ended September 30, 2016 and 2015, respectively, and $(2,126) and $2,852 for the nine months ended September 30, 2016 and 2015, respectively	260	(2,654)	(4,051)	4,858
Comprehensive loss	$ (14,116)	$ (18,334)	$ (53,456)	$ (36,254)