Derivative and Other Fair Value Instruments - Summary of Fair Value Measurements for Each Major Category of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Fair Value Of SERP Investments	$ 144,561	$ 140,159
Assets, Fair Value Disclosure	172,087	145,302
Other Liabilities, Fair Value Disclosure	144,561	140,159
Liabilities, Fair Value Disclosure	147,649	141,756
Redeemable Noncontrolling Interests - Operating Partnership/Redeemable Limited Partners	381,239	366,955
Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	3,088	1,597
Forward Starting Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	27,526	5,143
Fair Value, Inputs, Level 1 [Member]
Derivatives, Fair Value [Line Items]
Fair Value Of SERP Investments	144,561	140,159
Assets, Fair Value Disclosure	144,561	140,159
Other Liabilities, Fair Value Disclosure	144,561	140,159
Liabilities, Fair Value Disclosure	144,561	140,159
Redeemable Noncontrolling Interests - Operating Partnership/Redeemable Limited Partners	0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	0	0
Fair Value, Inputs, Level 1 [Member] | Forward Starting Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	0	0
Fair Value, Inputs, Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair Value Of SERP Investments	0	0
Assets, Fair Value Disclosure	27,526	5,143
Other Liabilities, Fair Value Disclosure	0	0
Liabilities, Fair Value Disclosure	3,088	1,597
Redeemable Noncontrolling Interests - Operating Partnership/Redeemable Limited Partners	381,239	366,955
Fair Value, Inputs, Level 2 [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	3,088	1,597
Fair Value, Inputs, Level 2 [Member] | Forward Starting Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	27,526	5,143
Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Fair Value Of SERP Investments	0	0
Assets, Fair Value Disclosure	0	0
Other Liabilities, Fair Value Disclosure	0	0
Liabilities, Fair Value Disclosure	0	0
Redeemable Noncontrolling Interests - Operating Partnership/Redeemable Limited Partners	0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	0	0
Fair Value, Inputs, Level 3 [Member] | Forward Starting Swaps [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	$ 0	$ 0