Description of Business and Significant Accounting Policies (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Description of Business and Significant Accounting Policies [Abstract]
In-service office, industrial and retail properties (in units)	302		302
Square footage of commercial property (in sq feet)	29,200,000		29,200,000
Rental residential units (in units)	96		96
Residential condominiums for sale (in units)	18		18
Undeveloped land suitable for future development (in acres)	601		601
Undeveloped land considered core holdings (in acres)	523		523
Office properties completed but not yet stabilized	1		1
Percentage of ownership of Common Units	95.10%		95.10%
Common Units of partnership owned by The Company	72,200,000		72,200,000
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)			43,308
Number of trading days preceeding Redemption Notice Date	10		10
Number of Common Stock Sold During Period (in shares)	142,000
Average Price of Common Stock Sold During Period	$ 34.21
Net Proceeds of Common Stock Sold During Period	$ 4,800,000
Excess of Preferred Stock redemption/repurchase cost over carrying value	$ 0	$ 0	$ 1,895,000	$ 0
Number of common units required to convert to one share of common stock (in shares)	1		1