Organization of The Parent Company and The Operating Partnership (Details)			12 Months Ended
	Dec. 31, 2011 managementcompanies A	Mar. 31, 2011	Dec. 31, 2011 Parent Company [Member] sqft A	Dec. 31, 2011 Unconsolidated real estate ventures [Member] sqft Real_Estate_Investments	Dec. 31, 2011 Wholly-owned management company subsidiaries [Member] sqft	Dec. 31, 2011 Third Parties and Unconsolidated Real Estate Ventures [Member] sqft	Dec. 31, 2011 Office Properties [Member] Properties	Dec. 31, 2011 Industrial facilities [Member] Properties	Dec. 31, 2011 Mixed-use properties [Member] Properties
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Ownership in the Operating Partnership	98.10%
Number of unconsolidated real estate ventures				18
Number of properties with ownership interest		3					207	20	5
Net rentable square feet			25,200,000	6,700,000	32,600,000	7,400,000
Number of Third-party real estate management services businesses that conduct business with Company	6
Ownership in Management Companies, directly and indirectly					100.00%
Area of undeveloped parcels of land (in acres) owned by a Real Estate Venture	4		444
Area of additional undeveloped parcels of land with option to purchase			52