Derivative Instruments - Cash flow hedges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Effects of derivative instruments
Amount of (Loss) Gain Recognized in OCI on Derivatives (Effective Portion)	$ (678)	$ (309)	$ (2,396)	$ 874
Cash Flow Hedging
Effects of derivative instruments
Amount of (Loss) Gain Recognized in OCI on Derivatives (Effective Portion)	(223)	221	(1,907)	1,636
Amount of Gain Recognized from Accumulated OCI into Income (Effective Portion)	119	113	516	182
Cash Flow Hedging | Interest rate contracts
Effects of derivative instruments
Amount of (Loss) Gain Recognized in OCI on Derivatives (Effective Portion)	(223)	221	(1,907)	1,636
Cash Flow Hedging | Interest rate contracts | Interest expense
Effects of derivative instruments
Amount of Gain Recognized from Accumulated OCI into Income (Effective Portion)	$ 119	$ 113	$ 516	$ 182