Environmental Obligations - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Jul. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Other Commitments [Line Items]
Payment for pollution legal liability insurance policy	$ 3,062,000
Pollution legal liability insurance policy duration		10 years
Pollution legal liability insurance policy aggregate limit		50,000,000
Remediation agreement of lease		We have agreed to be responsible for environmental contamination at the premises that was known at the time the lease commenced and for contamination that existed at the premises prior to commencement of the lease and is discovered (other than as a result of a voluntary site investigation) during the first ten years of the lease term.
Asset retirement obligations removed from balance sheet		13,074,000
Deferred rental revenue		2,441,000
Environmental remediation obligations		42,320,000		43,472,000
Accretion expense		2,032,000	2,119,000
The amounts of credits to environmental expenses included in continuing operations and to earnings from operating activities in discontinued operations		423,000	1,031,000
Increase in carrying value of property		7,801,000	8,657,000
Estimated remaining useful life of underground storage tank for capitalized asset retirement costs		10 years
Depreciation and amortization expense for capitalized asset retirement costs		1,078,000	1,648,000
Capitalized asset retirement costs		17,366,000		18,281,000
USTs [Member]
Other Commitments [Line Items]
Asset retirement obligations removed from balance sheet		13,074,000
Net asset cost related to USTs removed from the balance sheet		10,633,000
Deferred rental revenue		$ 2,441,000