Related Party Arrangements (Details) (USD $)	9 Months Ended		3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Unconsolidated real estate entities	Sep. 30, 2011 Unconsolidated real estate entities	Sep. 30, 2012 Unconsolidated real estate entities	Sep. 30, 2011 Unconsolidated real estate entities	Dec. 31, 2011 Unconsolidated real estate entities	Sep. 30, 2012 Non-employee directors Restricted stock and deferred stock awards	Sep. 30, 2012 Non-employee directors Restricted stock and deferred stock awards	Dec. 31, 2011 Non-employee directors Restricted stock and deferred stock awards
Related Party Arrangements
Asset management, property management, development and redevelopment fee revenue			$ 2,533,000	$ 2,433,000	$ 7,852,000	$ 7,085,000
Receivables associated with management fees			3,643,000		3,643,000		4,294,000
Compensation expense	8,394,000	7,614,000						240,000	669,000
Amount of deferred compensation									$ 576,000	$ 370,000