Condensed Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (35,793)	$ (18,550)	$ (97,869)	$ (58,290)
Other comprehensive loss:
Unrealized (loss) gain on available-for-sale securities, net of tax	(46)	100	(79)	31
Total comprehensive loss	$ (35,839)	$ (18,450)	$ (97,948)	$ (58,259)