Accounting for Interest Rate Swap Agreements (Details 2) (Derivatives designated as cash flow hedges, Interest rate hedges, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Derivatives designated as cash flow hedges | Interest rate hedges
Effect of derivative instruments on results of operations
Gain (Loss) Recognized in Other Comprehensive Income (Loss) on Derivatives	$ (5,542)	$ (14,601)
Gain (Loss) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss)	$ (4,761)	$ (13,961)