Derivative and Other Fair Value Instruments (Details 1) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	$ 114,123	$ 105,942
Assets, Fair Value Disclosure	124,656	109,597
Supplemental Executive Retirement Plan	114,123	105,942
Financial and Nonfinancial Liabilities, Fair Value Disclosure	117,702	106,615
Redeemable Noncontrolling Interests Operating Partnership	521,080	566,783
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)
Derivatives, Fair Value [Line Items]
Supplemental Executive Retirement Plan	114,123	105,942
Assets, Fair Value Disclosure	114,123	105,942
Supplemental Executive Retirement Plan	114,123	105,942
Financial and Nonfinancial Liabilities, Fair Value Disclosure	114,123	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	10,533	3,655
Supplemental Executive Retirement Plan	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	3,579	673
Redeemable Noncontrolling Interests Operating Partnership	521,080	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	10,533	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	10,533	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	3,579	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	3,579	673
Forward Starting Swaps | Significant Unobservable Inputs (Level 3)
Derivatives, Fair Value [Line Items]
Derivative Liability	$ 0	$ 0