Segment Information (Reportable Segment Information) (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Revenues	$ 141,225	$ 137,791	$ 275,320	$ 273,883
Net Operating Income	98,059	95,992	191,126	189,537
Equity in Earnings (Loss) of Real Estate Joint Ventures and Partnerships, net	3,579	2,630	6,976	5,866
Investment in Real Estate Joint Ventures and Partnerships, net	345,404		345,404		347,526
Total Assets	4,755,778		4,755,778		4,807,855
Shopping Center [Member]
Revenues	125,036	122,144	244,627	243,688
Net Operating Income	88,007	86,213	172,494	171,008
Equity in Earnings (Loss) of Real Estate Joint Ventures and Partnerships, net	3,439	2,457	6,763	5,636
Investment in Real Estate Joint Ventures and Partnerships, net	308,028		308,028		309,171
Total Assets	3,442,227		3,442,227		3,469,694
Industrial [Member]
Revenues	12,530	13,142	24,917	25,627
Net Operating Income	8,472	8,958	17,028	17,456
Equity in Earnings (Loss) of Real Estate Joint Ventures and Partnerships, net	286	319	432	525
Investment in Real Estate Joint Ventures and Partnerships, net	37,376		37,376		38,355
Total Assets	355,252		355,252		363,153
Other [Member]
Revenues	3,659	2,505	5,776	4,568
Net Operating Income	1,580	821	1,604	1,073
Equity in Earnings (Loss) of Real Estate Joint Ventures and Partnerships, net	(146)	(146)	(219)	(295)
Total Assets	$ 958,299		$ 958,299		$ 975,008