Environmental Matters (Details) (USD $)	1 Months Ended	3 Months Ended			6 Months Ended
	Jul. 31, 2012	Jun. 30, 2012	Dec. 31, 2011 Property	Jun. 30, 2011	Jun. 30, 2012 Site	Jun. 30, 2011	Dec. 31, 2010
Environmental Matters (Additional Textual) [Abstract]
Payment for pollution legal liability insurance policy	$ 3,000,000
Pollution legal liability insurance policy duration	10 years
Number of sites for which title to and obligations for USTs were transferred to new tenants					282
Asset retirement obligations removed from Balance Sheet					6,875,000
Deferred rental revenue		672,000			672,000
Increase in carrying value of property		2,232,000			3,691,000
Environmental remediation costs, net		52,263,000	57,700,000		52,263,000		14,874,000
Accretion expense					1,584,000	296,000
Environmental expenses, net		(564,000)		1,325,000	9,000	2,452,000
Number of properties for which Marketing would not be able to meet its environmental remediation obligations			246
Accrued Marketing environmental liabilities			47,874,000
Environmental costs, impairment charges		1,718,000	17,017,000		2,010,000
Underground Storage Tanks [Member]
Environmental Matters (Textual) [Abstract]
Net asset cost related to USTs removed from the Balance Sheet		6,203,000			6,203,000
Capitalized Asset Retirement Cost [Member]
Environmental Matters (Textual) [Abstract]
Depreciation and amortization expense for capitalized asset retirement costs		1,359,000			3,168,000
Maximum [Member]
Environmental Matters (Textual) [Abstract]
Pollution legal liability insurance policy aggregate limit	$ 50,000,000