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Derivative Financial Instruments Fair Value of the Company's Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
British pound forward contracts [Member] \| Designated as Hedging Instrument [Member] \| Other assets, net [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 7,320		$ 13,657
British pound forward contracts [Member] \| Designated as Hedging Instrument [Member] \| Other long-term liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	1,535		829
Cross-currency swap [Member] \| Not Designated as Hedging Instrument [Member] \| Other assets, net [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	3,239		2,887
Cross-currency swap [Member] \| Not Designated as Hedging Instrument [Member] \| Prepaid Expenses and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	12,956		5,775
Interest rate swap agreements [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	500	$ 400
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	1,000
Interest rate swap agreements [Member] \| Designated as Hedging Instrument [Member] \| Accrued expenses [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	975		1,972
Interest rate swap agreements [Member] \| Designated as Hedging Instrument [Member] \| Other long-term liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	4,327		12,410
Fair Value, Inputs, Level 2 [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	16,195		8,662
Fair Value, Inputs, Level 2 [Member] \| Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	7,320		13,657
Derivative Liability, Fair Value, Gross Liability	$ 6,837		$ 15,211