Segment Information (Reportable Segment Information) (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 138,565	$ 134,118	$ 405,617	$ 400,308
Net Operating Income	95,930	94,664	281,481	279,351
Equity in Earnings (Loss) of Real Estate Joint Ventures and Partnerships, net	(3,034)	3,455	3,942	9,321
Investment in Real Estate Joint Ventures and Partnerships, net	342,672		342,672		347,526
Total Assets	4,672,437		4,672,437		4,807,855
Shopping Center [Member]
Segment Reporting Information [Line Items]
Revenues	123,851	119,281	360,931	355,956
Net Operating Income	87,581	85,689	255,009	252,296
Equity in Earnings (Loss) of Real Estate Joint Ventures and Partnerships, net	(3,113)	3,297	3,650	8,933
Investment in Real Estate Joint Ventures and Partnerships, net	306,576		306,576		309,171
Total Assets	3,410,088		3,410,088		3,469,694
Industrial [Member]
Segment Reporting Information [Line Items]
Revenues	12,490	12,626	36,549	37,573
Net Operating Income	8,044	8,567	24,420	25,574
Equity in Earnings (Loss) of Real Estate Joint Ventures and Partnerships, net	92	227	524	752
Investment in Real Estate Joint Ventures and Partnerships, net	36,096		36,096		38,355
Total Assets	353,788		353,788		363,153
Other [Member]
Segment Reporting Information [Line Items]
Revenues	2,224	2,211	8,137	6,779
Net Operating Income	305	408	2,052	1,481
Equity in Earnings (Loss) of Real Estate Joint Ventures and Partnerships, net	(13)	(69)	(232)	(364)
Total Assets	$ 908,561		$ 908,561		$ 975,008