Acquisitions (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Lease commisions [Member]	Sep. 30, 2012 Lease in place value [Member]	Sep. 30, 2012 Above market leases [Member]	Sep. 30, 2012 Below market leases [Member]	Sep. 30, 2012 Other intangibles [Member]	Sep. 30, 2012 Buildings [Member]	Sep. 30, 2012 Tenant Improvements [Member]	Oct. 05, 2012 Westshore Corporate Center [Member] sqft	Oct. 31, 2012 NASCAR Plaza [Member] sqft	Jan. 11, 2012 The Pointe [Member] sqft	Feb. 10, 2012 Hayden Ferry Lakeside II [Member] sqft	Aug. 31, 2012 Hayden Ferry Garage [Member] sqft	Jun. 06, 2012 Hearst Tower [Member] sqft
Business Acquisition [Line Items]
Area of real estate property (in square feet)												170,000	390,000	252,000	300,000	21,000	972,000
Cost of entity acquired												$ 22,500,000	$ 100,000,000	$ 46,900,000	$ 86,000,000	$ 18,200,000	$ 250,000,000
Equity Contribution In A Business Combination														7,000,000	10,800,000	5,500,000
Preliminary allocation of purchase price [Abstract]
Land	21,969,000		21,969,000
Buildings & Garages	309,329,000		309,329,000
Tenant improvements	26,631,000		26,631,000
Lease commissions	10,141,000		10,141,000
Lease in place value	27,653,000		27,653,000
Above market leases	4,944,000		4,944,000
Below market leases	(3,729,000)		(3,729,000)
Other intangibles	3,001,000		3,001,000
Ownership percentage of property (in hundredths)														30.00%	30.00%
Number of parking spaces in garage acquired																2,500
Mortgage assumed in a business acquisition												14,500,000	42,300,000
Mortgage assumed in a business combinations interest rate												5.80%	4.70%
Property, Plant and Equipment [Line Items]
Weighted average life (in years)										40 years 0 months 0 days	6 years 0 months 0 days
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life (in years)					6 years 0 months 0 days	6 years 0 months 0 days	4 years 0 months 0 days	7 years 0 months 0 days	3 years 0 months 0 days
Business Acquisition, Pro Forma Revenue	59,757,000	58,986,000	179,774,000	146,604,000
Business Acquisition, Pro Forma Net Income (Loss)	$ (568,000)	$ (53,510,000)	$ 3,147,000	$ (71,482,000)
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ (0.02)	$ (2.49)	$ 0.15	$ (3.33)
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ (0.02)	$ (2.49)	$ 0.15	$ (3.33)