Derivatives Derivatives, Hedging Instruments, Consolidated Statement of Comprehensive Income (Details) (Interest rate swap [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Hedging instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI (Effective Portion)	$ (14,693)	$ (14,810)	$ (17,780)	$ (13,722)
Amount Reclassified from OCI into Net Income (Effective Portion)	3,509	3,072	6,775	4,941
Interest expense [Member] | Hedging instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount Reclassified from OCI into Net Income (Effective Portion)	3,509	3,072	6,775	4,941
Other Income, net [Member] | Hedging instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in Net Income (Ineffective Portion)	131	(25)	69	(24)
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	$ (500)	$ (871)	$ (574)	$ (1,204)