Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (276,011)	$ (239,284)	$ (141,965)
Other comprehensive income (loss)
Unrealized gain (loss) on available-for-sale securities	134	(52)	(98)
Comprehensive loss	$ (275,877)	$ (239,336)	$ (142,063)