Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	$ 162,091	$ 150,997
Real estate fund investments	566,696	574,761
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	162,091	150,997
Real estate fund investments	566,696	574,761
Deferred compensation plan assets (included in other assets)	116,824	117,475
Interest rate swap (included in other assets)	5,039
Total assets	850,650	843,233
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swaps (included in other liabilities)	28,914	19,600
Total liabilities	$ 79,475	$ 70,161
Other Partners Ownership Interest In Real Estate Fund (in percentage)	75.00%	75.00%
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real Estate, Net at Fair Value	$ 192,003
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	162,091	$ 150,997
Real estate fund investments	0	0
Deferred compensation plan assets (included in other assets)	59,640	58,289
Interest rate swap (included in other assets)	0
Total assets	221,731	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
Interest rate swap (included in other assets)	5,039
Total assets	5,039	0
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	28,914	19,600
Total liabilities	28,914	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	566,696	574,761
Deferred compensation plan assets (included in other assets)	57,184	59,186
Interest rate swap (included in other assets)	0
Total assets	623,880	633,947
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	0	$ 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real Estate, Net at Fair Value	$ 192,003