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Allocation of Recorded Value of Net Assets Acquired in Transaction (Detail) (USD $)
In Thousands, unless otherwise specified
Jun. 18, 2012
Dec. 28, 2011
Business Acquisition [Line Items]    
Proved oil and gas properties $ 39,221 $ 208,680
Unevaluated oil and gas properties 1,637 17,314
Asset retirement obligations (14,460) (58,363)
Total fair value of net assets $ 26,398 $ 167,631