Derivative Instruments Derivative gain loss table (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	$ 140	$ 211	$ 307	$ 424
Interest Rate Swap No. 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	94	130	202	261
Interest Rate Swap No. 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	$ 46	$ 81	$ 105	$ 163