Derivative Financial Instruments Derivative Instruments Designated as Hedges OCI Activity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Intercompany Loan [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) for mark-to-market of the U.K. intercompany loan	$ 16,700	$ (9,200)	$ 19,500	$ (3,700)
British pound forward contracts, net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	(15,600)	9,000	(18,000)	3,500
Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	(21,525)	2,701	(34,499)	9,603
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	(20,273)	2,701	(33,247)	9,603
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest rate swap agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	(21,299)	2,687	(34,705)	9,580
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign currency forward contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	0	288	0	288
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | British pound forward contracts, net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	1,026	(274)	1,458	(265)
Net Investment Hedging [Member] | Designated as Hedging Instrument [Member] | Cross-currency swap contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	(822)	0	(822)	0
Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Cross-currency swap contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	$ (430)	$ 0	$ (430)	$ 0