Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified from AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Settlement Gain (Loss) on Interest Rate Protection Agreements	$ 1,896	$ 0	$ (11,546)
Interest Expense - Amortization of IRPAs	57,199	59,430	67,424
Total	71,029	5,553	(33,223)
Interest Rate Swap | Reclassification out of Accumulated Other Comprehensive Loss | Interest Rate Protection Agreements
Accumulated Other Comprehensive Income (Loss) [Line Items]
Settlement Gain (Loss) on Interest Rate Protection Agreements	0	0	12,990
Interest Expense - Amortization of IRPAs	205	390	524
Interest Expense - Settlement Payments	4,336	7,123	5,529
Total	$ 4,541	$ 7,513	$ 19,043