Real Estate Activities (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Mar. 06, 2015 sqft	Mar. 19, 2015 sqft	Sep. 16, 2014 sqft	Dec. 19, 2014 sqft
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net loss	$ (5,902,000)	$ (29,657,000)
Proceeds from sale of discontinued operations	55,276,000	0
One & Two Chestnut Place Worcester Ma [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net Rentable Area				218,000
Contract Sale Price				14,000,000
Net loss	(87,000)	(10,000)
Proceeds from sale of discontinued operations	11,515,000
250 W Pratt Baltimore Md [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net Rentable Area					368,000
Contract Sale Price					63,500,000
Proceeds from sale of discontinued operations	55,276,000
City Hall Plaza Manchester Nh [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net Rentable Area						210,000
Contract Sale Price						19,750,000
Proceeds from sale of discontinued operations			19,130,000
222 South Riverside Plaza Chicago Illinois [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract price, cash portion							247,000,000
Net Rentable Area							1,184,000
Proceeds from sale of discontinued operations			223,670,000
Disposed Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net Rentable Area			1,394,000
Proceeds from sale of discontinued operations			$ 242,800,000