Derivative Financial Instruments Derivative Instruments Designated as Cash Flow Hedges OCI Activity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Intercompany Loan [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) for mark-to-market of the U.K. intercompany loan	$ 2,800	$ 5,500
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	(2,400)	(5,500)
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	(12,974)	6,901
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	(13,406)	6,892
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	$ 432	$ 9