Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Effects of derivative instruments
Amount of Gain Recognized in OCI on Derivatives (Effective Portion)	$ 458	$ (2,547)	$ 780	$ (2,021)
Cash Flow Hedging
Effects of derivative instruments
Amount of Gain Recognized in OCI on Derivatives (Effective Portion)	164		160
Amount of Loss (Gain) Reclassified from Accumulated OCI into Income (Effective Portion)	117		517
Cash Flow Hedging | Interest expense Member
Effects of derivative instruments
Amount of Loss (Gain) Reclassified from Accumulated OCI into Income (Effective Portion)	117		517
Cash Flow Hedging | Interest rate contracts | Interest expense Member
Effects of derivative instruments
Amount of Gain Recognized in OCI on Derivatives (Effective Portion)	$ 164		$ 160