Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2015

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]

(Amounts in thousands)		As of June 30, 2015
		Total		Level 1		Level 2		Level 3
Marketable securities		$	159,991	$	159,991	$	-	$	-
Real estate fund investments (75% of which is attributable to
	noncontrolling interests)		565,976		-		-		565,976
Deferred compensation plan assets (included in other assets)			118,932		51,264		-		67,668
	Total assets	$	844,899	$	211,255	$	-	$	633,644
Mandatorily redeemable instruments (included in other liabilities)		$	55,097	$	55,097	$	-	$	-
Interest rate swap (included in other liabilities)			23,747		-		23,747		-
	Total liabilities	$	78,844	$	55,097	$	23,747	$	-
(Amounts in thousands)		As of December 31, 2014
		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	$	-

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

(Amounts in thousands)	As of December 31, 2014
	Total		Level 1		Level 2		Level 3
Real estate assets	$	4,848	$	-	$	-	$	4,848

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

(Amounts in thousands)		As of June 30, 2015				As of December 31, 2014
		Carrying		Fair		Carrying		Fair
		Amount		Value		Amount		Value
Cash equivalents		$	311,017	$	311,000	$	749,418	$	749,000
Mortgage and mezzanine loans receivable			-		-		16,748		17,000
		$	311,017	$	311,000	$	766,166	$	766,000
Debt:
	Mortgages payable	$	8,562,314	$	8,541,000	$	8,263,165	$	8,224,000
	Senior unsecured notes		847,463		882,000		1,347,159		1,385,000
	Revolving credit facility debt		400,000		400,000		-		-
		$	9,809,777	$	9,823,000	$	9,610,324	$	9,609,000

Real Estate Fund [Member]

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

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

				Weighted Average
		Range		(based on fair value of investments)
Unobservable Quantitative Input		June 30, 2015	December 31, 2014	June 30, 2015	December 31, 2014
	Discount rates	12.0% to 14.5%	12.0% to 17.5%	13.4%	13.7%
	Terminal capitalization rates	4.8% to 6.5%	4.7% to 6.5%	5.5%	5.3%

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

(Amounts in thousands)	For the Three Months Ended June 30,				For the Six Months Ended June 30,
		2015		2014	2015		2014
Beginning balance	$	554,426	$	682,002	$	513,973	$	667,710
Purchases		-		2,544		95,000		2,667
Dispositions / Distributions		(11,235)		(232,513)		(83,421)		(232,513)
Net unrealized gains		23,332		57,354		39,545		58,546
Net realized gains		886		39,704		2,312		52,681
Other, net		(1,433)		-		(1,433)		-
Ending balance	$	565,976	$	549,091	$	565,976	$	549,091

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]

(Amounts in thousands)	For the Three Months Ended June 30,				For the Six Months Ended June 30,
		2015		2014	2015		2014
Beginning balance	$	64,836	$	67,627	$	63,315	$	68,782
Purchases		5,607		7,915		6,231		9,559
Sales		(4,655)		(11,255)		(5,093)		(16,379)
Realized and unrealized gain (loss)		1,387		(198)		2,722		1,974
Other, net		493		520		493		673
Ending balance	$	67,668	$	64,609	$	67,668	$	64,609