Derivatives Derivatives, Hedging Instruments, Consolidated Statement of Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment for interest expense amounts included in statement of income	$ 3,827	$ 3,383	$ 10,602	$ 8,325
Interest rate swap [Member] | Hedging instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	(11,073)	(18,251)	(28,853)	(31,974)
Interest rate swap [Member] | Interest expense [Member] | Hedging instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification adjustment for interest expense amounts included in statement of income	3,827		10,602
Amount Reclassified from OCI into Net Income (Effective Portion)		3,383		8,325
Interest rate swap [Member] | Other Income, net [Member] | Hedging instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in Net Income (Ineffective Portion)	(107)	(31)	(38)	(55)
Interest rate swap [Member] | Fair value adjustments, net [Member] | Designated as Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (333)	$ (1,446)	$ (907)	$ (2,649)