Accumulated Other Comprehensive Loss (Amounts Reclassified from AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest Expense - Amortization of IRPAs	$ 14,915	$ 14,589	$ 29,284	$ 30,848
Total	5,165	21,404	(3,626)	11,523
Interest Rate Swap | Reclassification out of Accumulated Other Comprehensive Income | Interest Rate Protection Agreements
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest Expense - Amortization of IRPAs	60	96	156	198
Interest Expense - Settlement Payments	1,161	1,815	2,574	3,651
Total	$ 1,221	$ 1,911	$ 2,730	$ 3,849