Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (72,865)	$ (70,972)
Other comprehensive loss
Unrealized gain (loss) on available-for-sale securities	(37)	176
Comprehensive loss	$ (72,902)	$ (70,796)