Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net [Rollforward]
Beginning balance	$ 1,855,578
Reclassification adjustment due to adoption of ASU 2016-01	(4,876)	$ 0
Ending Balance	1,823,264
Foreign currency
Accumulated Other Comprehensive Income (Loss), Net [Rollforward]
Beginning balance	(5,404)
Other comprehensive income (loss) before reclassifications	4,865
Reclassification adjustment due to adoption of ASU 2016-01	0
Net other comprehensive income (loss)	4,865
Ending Balance	(539)
Unrealized gain (loss) in Accumulated OCI
Accumulated Other Comprehensive Income (Loss), Net [Rollforward]
Beginning balance	4,876
Other comprehensive income (loss) before reclassifications	0
Reclassification adjustment due to adoption of ASU 2016-01	(4,876)
Net other comprehensive income (loss)	(4,876)
Ending Balance	0
AOCI Attributable to Parent
Accumulated Other Comprehensive Income (Loss), Net [Rollforward]
Beginning balance	(528)
Other comprehensive income (loss) before reclassifications	4,865
Reclassification adjustment due to adoption of ASU 2016-01	(4,876)
Net other comprehensive income (loss)	(11)
Ending Balance	$ (539)