Derivatives (Details 7) - Not designated as hedging - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Interest rate contract | Interest rate derivative gains (losses) included in Interest expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (losses) on derivatives	$ 1,286	$ 603
Foreign Exchange Contract | Other Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (losses) on derivatives	$ 539	$ (112)