Accounting for the Impairment or Disposal of Long-Lived Assets - Real Estate Impairments in Reportable Segments (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Schedule of Real Estate Impairment [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	$ 7,829,000		$ 957,000		$ 9,509,000
Northeast Southeastern PA [Member]
Schedule of Real Estate Impairment [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	0		(52,000)	[1]	0
Northeast Lehigh/Central PA [Member]
Schedule of Real Estate Impairment [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	0		0		113,000
Northeast Other [Member]
Schedule of Real Estate Impairment [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	538,000		0		1,138,000
Central Region [Member]
Schedule of Real Estate Impairment [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	5,990,000		511,000		837,000
South Region [Member]
Schedule of Real Estate Impairment [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	1,331,000		121,000		4,284,000
Metro [Member]
Schedule of Real Estate Impairment [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	$ (30,000)	[1]	$ 377,000		$ 3,137,000

[1] (1) Represents recovery of estimated sales costs on properties sold.