Related Party Arrangements (Details) (USD $)	3 Months Ended					3 Months Ended	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Unconsolidated real estate entities	Mar. 31, 2011 Unconsolidated real estate entities	Dec. 31, 2011 Unconsolidated real estate entities	Mar. 31, 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			$ 2,549,000	$ 2,320,000
Receivables associated with management fees			3,623,000		4,294,000
Compensation expense	2,974,000	2,834,000				209,000	187,000
Amount of deferred compensation						$ 161,000	$ 370,000