Fair Value Measurements - Reconciliation of Recurring Financial Liability Related to Interest Rate Swaps (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Cost of Hedge Net of Cash Received	$ (132)
Reconciliation of the recurring financial liability related to interest rate swaps
Derivative, Cash Received on Hedge		$ 54
Total gains/(losses) for the period:
Gain (Loss) on Foreign Currency Derivatives Recorded in Earnings, Net	(94)	36	$ 0
Foreign currency hedges | Designated as Hedging Instrument | Cash Flow Hedge
Reconciliation of the recurring financial liability related to interest rate swaps
Beginning balance	(601)	0
Total gains/(losses) for the period:
Included in earnings		(18)
Gain (Loss) on Foreign Currency Derivatives Recorded in Earnings, Net	38	(18)
Included in other comprehensive earnings	(47)	(637)
Ending balance	(742)	(601)	0
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedge
Reconciliation of the recurring financial liability related to interest rate swaps
Beginning balance	753	(768)
Total gains/(losses) for the period:
Included in earnings	(37)	928
Included in other comprehensive earnings	218	593
Ending balance		$ 753	$ (768)
Derivative Asset	$ (971)