Selected Financial Information Regarding Results of Operations of Charter Fleet Business (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Environmental costs recognized, recovery credited to expense	$ 2.0

Amount of any recovery from third parties that is credited to environmental remediation costs.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 12

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13296-110859

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration