CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (110,638)	$ (103,799)	$ (84,052)
Other comprehensive gain (loss), before tax:
Net unrealized loss on available-for-sale investments	(247)	(213)	(44)
Foreign currency translation gain (loss)	824	(488)	(942)
Net unrealized gain (loss) on derivative instruments	3,888	(2,271)	(711)
Other comprehensive gain (loss), before tax	4,465	(2,972)	(1,697)
Tax effect	(1,640)	0	0
Other comprehensive gain (loss), net of tax	2,825	(2,972)	(1,697)
Comprehensive loss	$ (107,813)	$ (106,771)	$ (85,749)