Accounting for the Impairment or Disposal of Long-Lived Assets - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Impaired Long-Lived Assets Held and Used [Line Items]
Proceeds from dispositions of operating properties	$ 228,500,000	$ 365,200,000	$ 29,000,000
Impairment charges	2,300,000	7,900,000	579,000
Asset Impairment Charges including amounts in Discontinued Operations	6,902,000	7,829,000	957,000
Other Asset Impairment Charges	4,597,000		378,000
Northeast Other [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	29,000	538,000	0
Central Region [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	566,000	5,990,000	511,000
South Region [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairment Charges including amounts in Discontinued Operations	$ 11,000	$ 1,331,000	$ 121,000