Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			$ 1,338,191	$ 1,093,628
Total changes in other comprehensive loss	$ (3,376)	$ (455)	(46,302)	(5,669)
Ending Balance	1,803,244	1,208,341	1,803,244	1,208,341
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(7,862)	(2,080)
Other comprehensive loss before reclassifications			(11,137)	(7,709)
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Total changes in other comprehensive loss			(11,137)	(7,709)
Ending Balance	(18,999)	(9,789)	(18,999)	(9,789)
Unrealized Holding Gains (Losses) on Marketable Securities, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			17,521	126
Other comprehensive loss before reclassifications			(7,786)	104
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Total changes in other comprehensive loss			(7,786)	104
Ending Balance	9,735	230	9,735	230
Unrealized Gains (Losses) on Foreign Currency Forward Contracts, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			11,514	3,778
Other comprehensive loss before reclassifications			(25,981)	6,715
Amounts reclassified from accumulated other comprehensive income (loss)			(1,398)	(4,779)
Total changes in other comprehensive loss			(27,379)	1,936
Ending Balance	(15,865)	5,714	(15,865)	5,714
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			21,173	1,824
Other comprehensive loss before reclassifications			(44,904)	(890)
Amounts reclassified from accumulated other comprehensive income (loss)			(1,398)	(4,779)
Total changes in other comprehensive loss			(46,302)	(5,669)
Ending Balance	$ (25,129)	$ (3,845)	$ (25,129)	$ (3,845)