Organization of The Parent Company and The Operating Partnership (Details)						9 Months Ended
	Sep. 30, 2011	Mar. 31, 2011 Property	Sep. 30, 2011 Office Properties [Member] Property	Sep. 30, 2011 Industrial facilities [Member] Property	Sep. 30, 2011 Mixed-use properties [Member] Property	Sep. 30, 2011 Parent Company [Member] sqft	Sep. 30, 2011 Unconsolidated real estate ventures [Member] sqft Property	Sep. 30, 2011 Wholly-owned management company subsidiaries [Member] sqft	Sep. 30, 2011 Third Parties and Unconsolidated Real Estate Ventures [Member] sqft
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Ownership in the Operating Partnership	93.20%
Number of unconsolidated real estate ventures							16
Total number of properties owned		3	211	20	5
Net rentable square feet						25,900,000	6,100,000	33,800,000	7,900,000