Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Equity [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	$ 15,061	$ (19,081)	$ (54,457)
Changes in the balances of each component of accumulated other comprehensive income
Accumulated Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Foreign Currency Translation, Net of Tax, Beginning Balance	(137,613)	(118,532)	(64,075)
Accumulated Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Foreign Currency Translation, Net of Tax, Ending Balance	(122,552)	(137,613)	(118,532)
Accumulated Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Interest Rate Swaps, Net of Tax, Beginning Balance	(9,331)	(19,452)	(17,909)
Interest rate swap contracts	8,657	10,121	(1,543)
Accumulated Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Interest Rate Swaps, Net of Tax, Ending Balance	(674)	(9,331)	(19,452)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	(146,944)	(137,984)	(81,984)
Other comprehensive income, net of tax	23,718	(8,960)	(56,000)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	$ (146,944)	$ (137,984)	$ (81,984)	$ (123,226)