Description of Business and Significant Accounting Policies (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Description of Business and Significant Accounting Policies [Abstract]
In-service office, industrial and retail properties (in units)	296		296
Square footage of commercial property (in sq feet)	27,300,000		27,300,000
Rental residential units (in units)	96		96
Residential condominiums for sale (in units)	19		19
Undeveloped land suitable for future development (in acres)	603		603
Undeveloped land considered core holdings (in acres)	523		523
Percentage of ownership of Common Units	95.00%		95.00%
Common Units of partnership owned by The Company	72,000,000		72,000,000
Common Units of partnership not owned by the Company	3,800,000		3,800,000
Common Stock par value	$ 0.01		$ 0.01		$ 0.01
Number of officers of the Company who are also limited partners	1		1
Number of directors of the Company who are also limited partners	2		2
Common units redeemed for a like number of common shares of stock (in shares)			18,737
Number of trading days preceeding Redemption Notice Date	10		10
Maximum Aggregate Offering Price of Common Stock Issuances			$ 150,000,000
Number of Common Stock Sold During Period (in shares)	236,000
Average Price of Common Stock Sold During Period	$ 35.62
Net Proceeds of Common Stock Sold During Period	8,300,000
Number of Preferred Stock Redeemed During Period (in shares)	2,100,000
Redemption Price of Preferred Stock Redeemed During Period	52,500,000
Excess of Preferred Stock redemption/repurchase cost over carrying value	$ 1,895,000	$ 0	$ 1,895,000	$ 0
Number of common units required to convert to one share of common stock (in shares)	1		1