Quarterly report pursuant to Section 13 or 15(d)

Acquisitions and Divestitures (Narrative) (Detail)

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Acquisitions and Divestitures (Narrative) (Detail) (USD $)
In Millions, unless otherwise specified
0 Months Ended 12 Months Ended
May 15, 2012
Jun. 30, 2012
May 11, 2011
Yellow Rose Properties
acre
Jun. 30, 2012
Fairway Properties
Aug. 10, 2011
Fairway Properties
Business Acquisition [Line Items]          
Percentage of non-operating working interest sold 40.00%        
Proceeds from sale of non-operating working interest $ 30.5        
Reversal of asset retirement obligation   4.0      
Number of acres of oil and gas leasehold interests acquired, gross     24,500    
Number of acres of oil and gas leasehold interests acquired, net     21,900    
Percentage of working interest include in producing interest         64.30%
Purchase price reduced       $ 3.7