Accounting for Derivatives (Details 2) (Derivatives designated as cash flow hedges, Interest rate hedges, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
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	$ 4,484	$ (2,405)	$ 4,700	$ (3,723)
Gain (Loss) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss)	$ (1,617)	$ (1,259)	$ (2,685)	$ (2,519)