Fair Value Measurements (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	$ 159,991	$ 206,323
Real Estate Fund Nondepreciable Real Estate	565,976	513,973
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	159,991	206,323
Real Estate Fund Nondepreciable Real Estate	565,976	513,973
Deferred Compensation Plan Assets	118,932	117,284
Total assets	844,899	837,580
Mandatorily redeemable instruments (included in other liabilities)	55,097	55,097
Interest rate swap (included in other liabilities)	23,747	25,797
Total liabilities	$ 78,844	$ 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	159,991	206,323
Real Estate Fund Nondepreciable Real Estate	0	0
Deferred Compensation Plan Assets	51,264	53,969
Total assets	211,255	260,292
Mandatorily redeemable instruments (included in other liabilities)	55,097	55,097
Interest rate swap (included in other liabilities)	0	0
Total liabilities	55,097	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)	23,747	25,797
Total liabilities	23,747	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	565,976	513,973
Deferred Compensation Plan Assets	67,668	63,315
Total assets	633,644	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