Derivatives - Amount of Gain (Loss) Recognized in OCI and Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) recognized in OCI	$ 881	$ (527)	$ 2,873	$ 310
Derivatives designated as cash flow hedges | Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) recognized in OCI	748	(893)	2,868	(507)
Derivatives designated as cash flow hedges | Interest rate swap | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) reclassified from AOCI	357	0	570	(104)
Derivatives designated as cash flow hedges | Foreign currency forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) recognized in OCI		353		741
Derivatives designated as cash flow hedges | Foreign currency forward contracts | Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) recognized in OCI	394		568
Amount of Gain/(Loss) reclassified from AOCI	(234)	(41)	(385)	(40)
Derivatives designated as cash flow hedges | Foreign currency forward contracts | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) reclassified from AOCI	$ 138	$ 28	$ 378	$ (37)