Accumulated Other Comprehensive Loss (Amounts Reclassified from AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest Expense - Amortization of IRPAs	$ 14,376	$ 14,407	$ 43,660	$ 45,255
Total	9,965	1,613	6,339	13,136
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	24	96	180	294
Interest Expense - Settlement Payments	912	1,774	3,486	5,425
Total	$ 936	$ 1,870	$ 3,666	$ 5,719