Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 3,581,956	$ 2,679,800
Other comprehensive income before reclassifications	975	28,137
Amounts reclassified from accumulated other comprehensive (loss) income		(129)
Net decrease in other comprehensive loss	975	28,008
Ending Balance	5,238,765	3,581,956
Foreign currency
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(20,557)	(47,966)
Other comprehensive income before reclassifications	975	27,409
Amounts reclassified from accumulated other comprehensive (loss) income		0
Net decrease in other comprehensive loss	975	27,409
Ending Balance	(19,582)	(20,557)
Change in unrealized gains on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	0	(599)
Other comprehensive income before reclassifications	0	728
Amounts reclassified from accumulated other comprehensive (loss) income		(129)
Net decrease in other comprehensive loss	0	599
Ending Balance	0	0
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(20,557)	(48,565)
Ending Balance	$ (19,582)	$ (20,557)