Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (480,129)	$ (539,215)	$ (443,790)
Change in net unrealized gains (losses) on available-for-sale investments, net of tax	483	(1,784)	(441)
Comprehensive loss	$ (479,646)	$ (540,999)	$ (444,231)