Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2014

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]

Schedule of Fair Values of Financial Assets and Liabilities by Levels [Table Text Block]

			As of December 31, 2014
(Amounts in thousands)			Total		Level 1		Level 2		Level 3
	Marketable securities		$	206,323	$	206,323	$	-	$	-
	Real Estate Fund investments (75% of which is attributable to
		noncontrolling interests)		513,973		-		-		513,973
	Deferred compensation plan assets (included in other assets)			117,284		53,969		-		63,315
		Total assets	$	837,580	$	260,292	$	-	$	577,288
	Mandatorily redeemable instruments (included in other liabilities)		$	55,097	$	55,097	$	-	$	-
	Interest rate swap (included in other liabilities)			25,797		-		25,797		-
		Total liabilities	$	80,894	$	55,097	$	25,797	$	-
			As of December 31, 2013
(Amounts in thousands)			Total		Level 1		Level 2		Level 3
	Marketable securities		$	191,917	$	191,917	$	-	$	-
	Real Estate Fund investments (75% of which is attributable to
		noncontrolling interests)		667,710		-		-		667,710
	Deferred compensation plan assets (included in other assets)			116,515		47,733		-		68,782
		Total assets	$	976,142	$	239,650	$	-	$	736,492
	Mandatorily redeemable instruments (included in other liabilities)		$	55,097	$	55,097	$	-	$	-
	Interest rate swap (included in other liabilities)			31,882		-		31,882		-
		Total liabilities	$	86,979	$	55,097	$	31,882	$	-

Fair Value Inputs, Assets, Quantitative Information [Table Text Block]

			Weighted Average
			(based on fair
Unobservable Quantitative Input		Range	value of investments)
	Discount rates	12.0% to 17.5%	13.7%
	Terminal capitalization rates	4.7% to 6.5%	5.3%

Non-financial Assets Measured at Fair Value on a Nonrecurring Basis [Table Text Block]

			As of December 31, 2014
(Amounts in thousands)			Total		Level 1		Level 2		Level 3
	Real estate assets		$	4,848	$	-	$	-	$	4,848
			As of December 31, 2013
(Amounts in thousands)			Total		Level 1		Level 2		Level 3
	Real estate assets		$	354,341	$	-	$	-	$	354,341
	Investment in Toys			83,224		-		-		83,224
		Total assets	$	437,565	$	-	$	-	$	437,565

Schedule Of Carrying Amounts And Fair Values Of Financial Instruments [Table Text Block]

				As of December 31, 2014				As of December 31, 2013
				Carrying		Fair		Carrying		Fair
(Amounts in thousands)				Amount		Value		Amount		Value
		Cash equivalents		$	749,418	$	749,000	$	295,000	$	295,000
		Mortgage and mezzanine loans receivable
			(included in other assets)		16,748		17,000		170,972		171,000
				$	766,166	$	766,000	$	465,972	$	466,000
	Debt:
		Mortgages payable		$	9,551,700	$	9,551,000	$	8,331,993	$	8,104,000
		Senior unsecured notes			1,347,159		1,385,000		1,350,855		1,402,000
		Revolving credit facility debt			-		-		295,870		296,000
				$	10,898,859	$	10,936,000	$	9,978,718	$	9,802,000

Real Estate Fund [Member]

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]

Summary of Changes in Level 3 Plan Assets [Table Text Block]

	Real Estate Fund Investments
	For The Year Ended December 31,
(Amounts in thousands)	2014		2013
Beginning balance	$	667,710	$	600,786
Purchases		3,392		43,816
Dispositions / Distributions		(307,268)		(70,848)
Net unrealized gains		73,802		85,771
Net realized gains		76,337		8,184
Other, net		-		1
Ending balance	$	513,973	$	667,710

Deferred Compensation Plan Assets [Member]

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]

Summary of Changes in Level 3 Plan Assets [Table Text Block]

	Deferred Compensation Plan Assets
	For The Year Ended December 31,
(Amounts in thousands)	2014		2013
Beginning balance	$	68,782	$	62,631
Purchases		14,162		5,018
Sales		(24,951)		(7,306)
Realized and unrealized gains		3,415		7,189
Other, net		1,907		1,250
Ending balance	$	63,315	$	68,782