Derivative Financial Instruments Derivative Instruments Designated as Cash Flow Hedges OCI Activity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Intercompany Loan [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) for mark-to-market of the U.K. intercompany loan	$ (9,200)	$ 3,800	$ (3,700)	$ 5,400
British Pound 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	9,000	(2,800)	3,500	(3,800)
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	2,702	(604)	9,603	(98)
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	2,688	(1,647)	9,580	(1,770)
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Currency Forward [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of net changes in fair value recognized in OCI, net of tax	288	0	288	0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | British Pound 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	$ (274)	$ 1,043	$ (265)	$ 1,672