Consolidated Statements of Cash Flows (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Cash Flows from Operating Activities:
Net income	$ 125,246,000	$ 98,156,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization (including amortization of deferred financing costs)	131,112,000	153,869,000
Return of capital from real estate fund investments	72,208,000	0
Net gains on sale of real estate and other	(32,243,000)	0
Straight-lining of rental income	(29,474,000)	(13,236,000)
Net realized and unrealized gains on real estate fund investments	(17,639,000)	(14,169,000)
Distributions of income from partially owned entities	15,874,000	12,966,000
Other non-cash adjustments	15,865,000	11,885,000
Amortization of below-market leases, net	(12,754,000)	(12,144,000)
(Loss) income from partially owned entities	2,405,000	(1,979,000)
Net gain on disposition of wholly owned and partially owned assets	(1,860,000)	(9,635,000)
Impairment losses	256,000	20,842,000
Changes in operating assets and liabilities:
Real estate fund investments	(95,022,000)	(123,000)
Accounts receivable, net	975,000	(7,624,000)
Prepaid assets	62,658,000	53,841,000
Other assets	(13,093,000)	(18,297,000)
Accounts payable and accrued expenses	(12,691,000)	31,554,000
Other liabilities	(17,307,000)	3,225,000
Net cash provided by operating activities	194,516,000	309,131,000
Cash Flows from Investing Activities:
Proceeds from sales of real estate and related investments	334,725,000	120,270,000
Development costs and construction in progress	(88,052,000)	(90,653,000)
Additions to real estate	(54,466,000)	(53,103,000)
Acquisitions of real estate and other	(49,878,000)	0
Investments in partially owned entities	(23,912,000)	(16,633,000)
Proceeds from repayments of mortgage and mezzanine loans receivable and other	16,763,000	69,347,000
Distributions of capital from partially owned entities	13,409,000	1,277,000
Restricted cash	1,282,000	52,256,000
Net cash provided by investing activities	149,871,000	82,761,000
Cash Flows from Financing Activities:
Repayments of borrowings	(907,431,000)	(233,198,000)
Proceeds from borrowings	800,000,000	600,000,000
Cash included in the spin-off of Urban Edge Properties	(225,000,000)	0
Dividends paid on common shares	(118,447,000)	(136,761,000)
Distributions to noncontrolling interests	(60,287,000)	(10,474,000)
Contributions from noncontrolling interests	51,350,000	0
Dividends paid on preferred shares	(19,484,000)	(20,368,000)
Proceeds received from exercise of employee share options	12,018,000	3,676,000
Debt issuance costs	(5,076,000)	(20,752,000)
Repurchase of shares related to stock compensation agreements and/or related tax withholdings	(2,939,000)	(578,000)
Net cash (used in) provided by financing activities	(475,296,000)	181,545,000
Net (decrease) increase in cash and cash equivalents	(130,909,000)	573,437,000
Cash and cash equivalents at beginning of period	1,198,477,000	583,290,000
Cash and cash equivalents at end of period	1,067,568,000	1,156,727,000
Supplemental Disclosure Of Cash Flow Information:
Cash payments for interest, excluding capitalized interest of $8,479 and $13,622	91,702,000	100,209,000
Cash payments for income taxes	2,175,000	1,214,000
Non-cash distribution of Urban Edge Properties:
Assets	1,722,263,000	0
Liabilities	(1,482,660,000)	0
Equity	(239,603,000)	0
Transfer of interest in real estate to Pennsylvania Real Estate Investment Trust	(145,313,000)	0
Accrued capital expenditures included in accounts payable and accrued expenses	87,232,000	74,424,000
Financing assumed in acquisitions	62,000,000	0
Adjustments to carry redeemable Class A units at redemption value	25,349,000	(136,937,000)
Receipt of security deposits included in restricted cash and other liabilities	42,346,000	0
Write-off of fully depreciated assets	(18,790,000)	(67,204,000)
Elimination of a mortgage and mezzanine loan asset and liability	0	59,375,000
Acquisitions [Member]
Non-cash distribution of Urban Edge Properties:
Like-kind exchange of real estate	57,722,000	0
Dispositions [Member]
Non-cash distribution of Urban Edge Properties:
Like-kind exchange of real estate	$ (38,822,000)	$ 0