Properties, net (Details) (USD $)			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Greater Philadelphia	Mar. 31, 2014 Operating properties, net	Dec. 31, 2013 Operating properties, net	Mar. 31, 2014 Operating properties, net Land	Dec. 31, 2013 Operating properties, net Land	Mar. 31, 2014 Operating properties, net Buildings and improvements	Dec. 31, 2013 Operating properties, net Buildings and improvements
Properties
Gross						$ 436,381,000	$ 430,472,000	$ 2,927,800,000	$ 2,869,870,000
Less: accumulated depreciation				(635,178,000)	(597,649,000)
Operating properties, net	2,729,003,000	2,702,693,000
Depreciation Expense on Reclassified Assets			$ 12,900,000