Derivative Instruments - Designated as hedging, Financial Position (Details) - Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cross Currency Interest Rate Contract [Member] | Net Investment Hedging [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ (4,110)
Cross Currency Interest Rate Contract [Member] | Net Investment Hedging [Member] | Other long-term liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	(4,110)	$ 0
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives		(4,070)
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Prepaid Expenses and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0	160
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	0	(870)
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Other long-term liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 0	$ (3,360)