Derivatives - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance Sheet Location and Fair Value
Long-term debt	$ (15,088)	$ (9,123)
Derivative Liabilities	4,264	4,712
Derivative Assets	980	9,418
Interest Rate Swaps \| Designated Hedges \| Current financial assets
Balance Sheet Location and Fair Value
Derivative Assets	479	1,079
Interest Rate Swaps \| Fair Value Hedges \| Designated Hedges
Balance Sheet Location and Fair Value
Derivative Liabilities		4,586
Derivative Assets	(135)
Interest Rate Swaps \| Fair Value Hedges \| Designated Hedges \| Non-current financial liabilities
Balance Sheet Location and Fair Value
Non-current financial liabilities	14,953	13,709
Interest Rate Swaps \| Fair Value Hedges \| Designated Hedges \| Long-term debt
Balance Sheet Location and Fair Value
Long-term debt	(15,088)	(9,123)
Foreign Currency Forward Contracts \| Non-designated Hedges \| Current financial assets
Balance Sheet Location and Fair Value
Derivative Assets	501	4,965
Foreign Currency Forward Contracts \| Non-designated Hedges \| Current financial liabilities
Balance Sheet Location and Fair Value
Derivative Liabilities	2,037	126
Foreign Currency Forward Contracts \| Cash Flow Hedging \| Designated Hedges \| Current financial assets
Balance Sheet Location and Fair Value
Derivative Assets	0	3,374
Foreign Currency Forward Contracts \| Cash Flow Hedging \| Designated Hedges \| Current financial liabilities
Balance Sheet Location and Fair Value
Derivative Liabilities	$ 2,362	$ 0

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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