Derivative and Other Fair Value Instruments (Details 1) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	$ 96,823	$ 104,463
Total derivative assets designated as hedging instruments	106,582	106,392
Supplemental Executive Retirement Plan	96,823	104,463
Total derivative liabilities designated as hedging instruments	97,918	118,567
Redeemable Noncontrolling Interests Operating Partnership	522,585	500,733
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	96,823	104,463
Total derivative assets designated as hedging instruments	96,823	104,463
Supplemental Executive Retirement Plan	96,823	104,463
Total derivative liabilities designated as hedging instruments	96,823	104,463
Redeemable Noncontrolling Interests Operating Partnership	0	0
Significant Other Observable Inputs (Level 2)
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	0	0
Total derivative assets designated as hedging instruments	9,759	1,929
Supplemental Executive Retirement Plan	0	0
Total derivative liabilities designated as hedging instruments	1,095	14,104
Redeemable Noncontrolling Interests Operating Partnership	522,585	500,733
Significant Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	0	0
Total derivative assets designated as hedging instruments	0	0
Supplemental Executive Retirement Plan	0	0
Total derivative liabilities designated as hedging instruments	0	0
Redeemable Noncontrolling Interests Operating Partnership	0	0
Fair Value Hedges
Derivatives, Fair Value [Line Items]
Derivative Asset	9,759	1,597
Fair Value Hedges | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)
Derivatives, Fair Value [Line Items]
Derivative Asset	0	0
Fair Value Hedges | Significant Other Observable Inputs (Level 2)
Derivatives, Fair Value [Line Items]
Derivative Asset	9,759	1,597
Fair Value Hedges | Significant Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Derivative Asset	0	0
Forward Starting Swaps
Derivatives, Fair Value [Line Items]
Derivative Asset		332
Derivative Liability	1,095	14,104
Forward Starting Swaps | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)
Derivatives, Fair Value [Line Items]
Derivative Asset		0
Derivative Liability	0	0
Forward Starting Swaps | Significant Other Observable Inputs (Level 2)
Derivatives, Fair Value [Line Items]
Derivative Asset		332
Derivative Liability	1,095	14,104
Forward Starting Swaps | Significant Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Derivative Asset		0
Derivative Liability	$ 0	$ 0