Derivative Instruments (Details 1) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Interest rate swaps [Member] | Interest Expense [Member] | Cash Flow Hedge [Member]
Effects of cash flow and fair value hedge derivative instruments on the accompanying Condensed Consolidated Statements of Comprehensive Income
Gain (loss) reclassified from Accumulated OCI (effective portion)	$ (6,678)	$ (4,997)	$ (8,672)	$ (9,895)
Interest rate swaps [Member] | Interest Expense [Member] | Fair Value Hedge [Member]
Effects of cash flow and fair value hedge derivative instruments on the accompanying Condensed Consolidated Statements of Comprehensive Income
Gain (loss) recognized in income	(7,419)	0	(7,419)	0
Interest rate swaps [Member] | Cash Flow Hedge [Member]
Effects of cash flow and fair value hedge derivative instruments on the accompanying Condensed Consolidated Statements of Comprehensive Income
Gain (loss) recognized in OCI (effective portion)	0	234	0	(574)
Fixed rate debt [Member] | Interest Expense [Member] | Fair Value Hedge [Member]
Effects of cash flow and fair value hedge derivative instruments on the accompanying Condensed Consolidated Statements of Comprehensive Income
Gain (loss) recognized in income	$ 7,419	$ 0	$ 7,419	$ 0