Fair Value Measurements (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	$ 152,927	$ 206,323
Real Estate Fund Nondepreciable Real Estate	555,414	513,973
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	152,927	206,323
Real Estate Fund Nondepreciable Real Estate	555,414	513,973
Deferred Compensation Plan Assets	117,037	117,284
Total assets	825,378	837,580
Mandatorily redeemable instruments (included in other liabilities)	53,135	55,097
Interest rate swap (included in other liabilities)	24,014	25,797
Total liabilities	$ 77,149	$ 80,894
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]
Total assets	$ 0
Real Estate, Net at Fair Value		$ 4,848
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	152,927	206,323
Real Estate Fund Nondepreciable Real Estate	0	0
Deferred Compensation Plan Assets	48,829	53,969
Total assets	201,756	260,292
Mandatorily redeemable instruments (included in other liabilities)	53,135	55,097
Interest rate swap (included in other liabilities)	0	0
Total liabilities	53,135	55,097
Fair Value, Inputs, Level 1 [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		0
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 Nondepreciable Real Estate	0	0
Deferred Compensation Plan Assets	0	0
Total assets	0	0
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)	24,014	25,797
Total liabilities	24,014	25,797
Fair Value Inputs Level 2 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		0
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 Nondepreciable Real Estate	555,414	513,973
Deferred Compensation Plan Assets	68,208	63,315
Total assets	623,622	577,288
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (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		$ 4,848