Fair Value of Financial Instruments Financial Instruments Carried at Fair Value-Level 2 (Details) - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets carried at fair value	$ 23,515	$ 22,319
Financial liabilities carried at fair value	6,837	15,211
Designated as Hedging Instrument [Member] | British pound forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	7,320	13,657
Derivative Liability	1,535	829
Designated as Hedging Instrument [Member] | Interest rate swap agreements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	5,302	14,382
Not Designated as Hedging Instrument [Member] | Cross-currency swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	$ 16,195	$ 8,662