Fair Value of Financial Instruments Financial Instruments Carried at Fair Value-Level 2 (Details) - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets carried at fair value	$ 20,800	$ 27,039
Financial liabilities carried at fair value	18,065	15,175
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	20,287	26,359
Derivative Liability	234	17
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	17,831	15,158
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	$ 513	$ 680