Real Estate Partnerships (Summarized Operating Results and Financial Position of Partnership) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Real Estate Partnerships Operating Results [Line Items]
Revenue	$ 141,466	[1]	$ 137,664	[1]	$ 136,279	[1]	$ 137,650	[1]	$ 137,334	[1]	$ 133,446	[1]	$ 133,216	[1]	$ 137,801	[1]	$ 553,059	$ 541,797	$ 528,569
Depreciation and amortization																	126,208	118,878	114,443
Interest expense																	98,465	101,882	108,781
NET INCOME	32,455		48,302	[2]	36,471		32,384		34,305		31,010		32,368		30,554		149,612	128,237	103,872
Income from real estate partnerships																	1,808	1,060	1,322
Real estate, net	3,306,956								2,860,738								3,306,956	2,860,738
Cash	67,806								15,797								67,806	15,797	135,389	15,223
TOTAL ASSETS	3,659,908								3,159,553								3,659,908	3,159,553
Mortgages payable	747,523								529,501								747,523	529,501
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	3,659,908								3,159,553								3,659,908	3,159,553
Our investment in real estate partnership	34,352								51,606								34,352	51,606
Federal / Lion Venture LP [Member]
Real Estate Partnerships Operating Results [Line Items]
Revenue																	19,289	18,639	19,109
Other operating expenses																	5,593	6,149	6,019
Depreciation and amortization																	5,179	5,046	4,998
Interest expense																	3,388	3,400	4,430
Total expenses																	14,160	14,595	15,447
NET INCOME																	5,129	4,044	3,662
Income from real estate partnerships																	1,771	1,449	1,322
Real estate, net	178,693								181,565								178,693	181,565
Cash	3,035								3,054								3,035	3,054
Other assets	6,116								7,336								6,116	7,336
TOTAL ASSETS	187,844								191,955								187,844	191,955
Mortgages payable	57,376								57,584								57,376	57,584
Other liabilities	5,391								5,439								5,391	5,439
Partners' capital	125,077								128,932								125,077	128,932
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	187,844								191,955								187,844	191,955
Our share of unconsolidated debt	17,213								17,275								17,213	17,275
Our investment in real estate partnership	$ 34,352								$ 35,504								$ 34,352	$ 35,504

[1] Revenue has been reduced to reflect the results of discontinued operations. Revenue from discontinued operations, by quarter, is summarized as follows: FirstQuarter SecondQuarter ThirdQuarter FourthQuarter (In thousands)2011 revenue from discontinued operations$978 $1,048 $163 $932010 revenue from discontinued operations$669 $619 $618 $1,627

[2] Third quarter 2011 amounts include a $14.8 million gain on sale of our Feasterville Shopping Center as further discussed in Note 3.