Accumulated Other Comprehensive Income (Amounts Reclassified from AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income [Line Items]
Interest Expense - Amortization of IRPAs	$ 12,424	$ 14,376	$ 37,818	$ 43,660
Total	(5,139)	9,965	12,884	6,339
Interest Rate Swap | Reclassification out of Accumulated Other Comprehensive Income | Interest Rate Protection Agreements
Accumulated Other Comprehensive Income [Line Items]
Interest Expense - Amortization of IRPAs	24	24	71	180
Interest Expense - Settlement Payments	(102)	912	458	3,486
Total	$ (78)	$ 936	$ 529	$ 3,666