CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (302,139)	$ (245,874)	$ (145,618)
Other comprehensive income (loss):
Foreign currency translation adjustments	(10,110)	1,322
Transfer of currency translation adjustments balance to other income for the liquidation of a foreign entity	3,490
Unrealized gain (loss) on available-for-sale securities	35	451	(694)
Other comprehensive income (loss):	(6,585)	1,773	(694)
Total comprehensive loss	$ (308,724)	$ (244,101)	$ (146,312)