Allocation of Recorded Value of Net Assets Acquired in Transaction (Detail) (USD $) In Millions, unless otherwise specified	Jun. 18, 2012
Business Combinations [Abstract]
Proved oil and gas properties	$ 39.2
Unevaluated oil and gas properties	1.6
Asset retirement obligations	(14.4)
Total fair value of net assets	$ 26.4

Business acquisition purchase price allocation asset retirement obligations.

No definition available.

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- Definition

Business acquisition purchase price allocation proved oil and gas properties.

+ References

No definition available.

+ Details

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- Definition

Business acquisition purchase price allocation unevaluated oil and gas properties.

+ References

No definition available.

+ Details

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- Definition

Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 55

-Paragraph 37

-URI http://asc.fasb.org/extlink&oid=25498275&loc=d3e2207-128464

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