Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	$ 194,489	$ 150,997
Real estate fund investments	524,150	574,761
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	194,489	150,997
Real estate fund investments	524,150	574,761
Deferred compensation plan assets (included in other assets)	119,292	117,475
Total assets	837,931	843,233
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swaps (included in other liabilities)	31,900	19,600
Total liabilities	82,461	70,161
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	194,489	150,997
Real estate fund investments	0	0
Deferred compensation plan assets (included in other assets)	59,152	58,289
Total assets	253,641	209,286
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	50,561	50,561
Fair Value Inputs Level 2 Member | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Real estate fund investments	0	0
Deferred compensation plan assets (included in other assets)	0	0
Total assets	0	0
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	31,900	19,600
Total liabilities	31,900	19,600
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Real estate fund investments	524,150	574,761
Deferred compensation plan assets (included in other assets)	60,140	59,186
Total assets	584,290	633,947
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	$ 0	$ 0