Derivative and Other Fair Value Instruments (Details 1) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	$ 116,287	$ 105,942
Assets, Fair Value Disclosure	128,332	109,597
Supplemental Executive Retirement Plan	116,287	105,942
Financial and Nonfinancial Liabilities, Fair Value Disclosure	121,427	106,615
Redeemable Noncontrolling Interests – Operating Partnership	478,324	566,783
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	116,287	105,942
Assets, Fair Value Disclosure	116,287	105,942
Supplemental Executive Retirement Plan	116,287	105,942
Financial and Nonfinancial Liabilities, Fair Value Disclosure	116,287	105,942
Redeemable Noncontrolling Interests – Operating Partnership	0	0
Significant Other Observable Inputs (Level 2)
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	0	0
Assets, Fair Value Disclosure	12,045	3,655
Supplemental Executive Retirement Plan	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	5,140	673
Redeemable Noncontrolling Interests – Operating Partnership	478,324	566,783
Significant Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	0	0
Assets, Fair Value Disclosure	0	0
Supplemental Executive Retirement Plan	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Redeemable Noncontrolling Interests – Operating Partnership	0	0
Fair Value Hedges
Derivatives, Fair Value [Line Items]
Derivative Asset	12,045	3,655
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	12,045	3,655
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 Liability	5,140	673
Forward Starting Swaps | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)
Derivatives, Fair Value [Line Items]
Derivative Liability	0	0
Forward Starting Swaps | Significant Other Observable Inputs (Level 2)
Derivatives, Fair Value [Line Items]
Derivative Liability	5,140	673
Forward Starting Swaps | Significant Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Derivative Liability	$ 0	$ 0