Accumulated Other Comprehensive Income (Amounts Reclassified from AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income [Line Items]
Interest Expense - Amortization of IRPAs	$ 12,603	$ 14,915	$ 25,394	$ 29,284
Total	11,619	5,165	18,023	(3,626)
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	23	60	47	156
Interest Expense - Settlement Payments	97	1,161	560	2,574
Total	$ 120	$ 1,221	$ 607	$ 2,730