Debt Interest Rate Swaps 2 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Gain on cash flow hedge ineffectiveness	$ 2,400		$ 600
Loss on Cash Flow Hedge Ineffectiveness		$ (100)
Cumulative fair value of de-designated cash flow hedges, gross	(1,400)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	1,900	$ 400
Interest Rate Swap 6, Credit Facility [Member]
Derivative [Line Items]
Interest rate swap agreement, notional amount	$ 75,000
Interest rate swap agreement, fixed interest rate	2.273%
Interest Rate Swap 7, Credit Facility [Member]
Derivative [Line Items]
Interest rate swap agreement, notional amount	$ 25,000
Interest rate swap agreement, fixed interest rate	2.111%
Interest Rate Swap 8, Credit Facility [Member]
Derivative [Line Items]
Interest rate swap agreement, notional amount	$ 50,000
Interest rate swap agreement, fixed interest rate	2.111%