Derivative Financial Instruments Derivative Instruments Designated as Cash Flow Hedges OCI Activity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Intercompany Loan [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) for mark-to-market of the U.K. intercompany loan	$ (1,700)	$ 3,200	$ (5,400)	$ 8,600
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	2,000	(2,800)	5,500	(6,600)
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	5,153	736	14,756	638
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	4,816	388	14,396	(1,382)
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	(13)	0	275	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	$ 350	$ 348	$ 85	$ 2,020