Derivative and Other Fair Value Instruments (Details 3) (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Schedule of Location of Fair Value/Cash flow Hedges on Statement of Operations
Effective Portion - Amount of Gain/ (Loss) Recognized in OCI on Derivative	$ (25,119)	$ (85,746)
Effective Portion - Amount of Gain/ (Loss) Reclassified from Accumulated OCI into Income	(1,891)	(1,465)
Ineffective Portion - Amount of Gain/ (Loss) Reclassified from Accumulated OCI into Income	(2,569)
Forward Starting Swaps/Treasury Locks [Member]
Schedule of Location of Fair Value/Cash flow Hedges on Statement of Operations
Effective Portion - Amount of Gain/ (Loss) Recognized in OCI on Derivative	(26,441)	(86,530)
Forward Starting Swaps/Treasury Locks [Member] | Interest Expense [Member]
Schedule of Location of Fair Value/Cash flow Hedges on Statement of Operations
Effective Portion - Amount of Gain/ (Loss) Reclassified from Accumulated OCI into Income	(1,891)	(1,465)
Ineffective Portion - Amount of Gain/ (Loss) Reclassified from Accumulated OCI into Income	(2,569)
Development Interest Rate Swaps/Caps [Member]
Schedule of Location of Fair Value/Cash flow Hedges on Statement of Operations
Effective Portion - Amount of Gain/ (Loss) Recognized in OCI on Derivative	$ 1,322	$ 784