Discontinued Operations (Details) (USD $)	3 Months Ended		6 Months Ended		0 Months Ended		6 Months Ended				0 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Mar. 20, 2013 Atrium at Stoneridge [Member] sqft		Jun. 30, 2013 Atrium at Stoneridge [Member]		Jun. 30, 2013 Waterstone and Meridian [Member] Property sqft		Jul. 10, 2013 Subsequent Event [Member] Waterstone and Meridian [Member] Property sqft	Jul. 17, 2013 Subsequent Event [Member] Bank of America Plaza [Member] sqft
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross sales price of assets sold					$ 3,100,000
Gain on sale of real estate from discontinued operations	0	3,197,000	542,000	8,772,000			542,000	[1]				11,900,000
Net proceeds from the sale					3,000,000
Area of real estate property (in square feet)					108,000	[1]			190,000	[2]
Date of Sale							Mar. 20, 2013	[1]
Number of properties under agreement to sell									2		2
Gross sales price of assets under agreement to sell									10,200,000	[2]	10,200,000	42,800,000
Impairment loss on assets to be disposed of											(4,600,000)
Proceeds from sale of property											$ 9,500,000	$ 40,800,000
Area of real estate property held for sale (in sqf)											190,000	436,000

[1] Total gain on the sale of real estate in discontinued operations recognized during the six months ended June 30, 2013 was $542,000.

[2] Gains and losses on assets held for sale are expected to be finalized upon sale and reflected in the nine months ended September 30, 2013 financial statements.