Quarterly report pursuant to Section 13 or 15(d)

Properties, net (Details)

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Properties, net (Details) (USD $)
6 Months Ended
Jun. 30, 2014
Dec. 31, 2013
Jun. 30, 2014
Greater Philadelphia
Jun. 30, 2014
Operating properties, net
Dec. 31, 2013
Operating properties, net
Jun. 30, 2014
Operating properties, net
Land
Dec. 31, 2013
Operating properties, net
Land
Jun. 30, 2014
Operating properties, net
Buildings and improvements
Dec. 31, 2013
Operating properties, net
Buildings and improvements
Investments in real estate                  
Gross           $ 433,362,000 $ 430,472,000 $ 2,946,094,000 $ 2,869,870,000
Less: accumulated depreciation       (655,214,000) (597,649,000)        
Operating properties, net 2,724,242,000 2,702,693,000              
Depreciation Expense on Reclassified Assets     $ 12,900,000