Quarterly report pursuant to Section 13 or 15(d)

Acquisitions and Divestitures - Additional Information (Detail)

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Acquisitions and Divestitures - Additional Information (Detail) (USD $)
 1 Months Ended 3 Months Ended 1 Months Ended 3 Months Ended 1 Months Ended
May 15, 2012
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Oct. 05, 2012
Newfield Properties
acre
Mar. 31, 2013
Newfield Properties
Mar. 31, 2012
Newfield Properties
Oct. 05, 2012
Newfield Properties
Overriding Royalty Interests
Business Acquisition [Line Items]                
Total cash paid for acquisition         $ 205,614,000      
Number of federal offshore blocks         78      
Leasehold interest acres acquired, gross         416,000      
Leasehold interest acres acquired, net         268,000      
Number of deep water federal offshore blocks         65     3
Number of productive deep water federal offshore blocks         6     2
Number of conventional shelf blocks         10      
Number of producing conventional shelf blocks         4      
Business acquisition, incremental revenue   259,222,000 235,886,000     28,600,000 43,200,000  
Business acquisition, direct operating expenses   59,341,000 56,663,000     6,600,000 11,300,000  
Business acquisition, incremental depreciation depletion amortization and accretion   108,872,000 88,491,000     10,500,000 20,400,000  
Business acquisition, incremental income tax expense estimation   14,902,000 1,981,000     4,000,000 2,700,000  
Net income   26,618,000 3,218,000     7,500,000    
Business acquisition, incremental insurance costs estimation             200,000  
Purchase price allocation of unevaluated properties for oil and gas interests   125,485,000   123,503,000     13,100,000  
Assumed borrowings   1,060,079,000   1,087,611,000     205,600,000  
Effective interest rate             7.70%  
Business acquisition, incremental interest expense estimation   21,234,000 13,905,000       4,000,000  
Business acquisition, incremental capitalized interest estimation   2,433,000 3,191,000       200,000  
Federal statutory income tax rate   35.00%         35.00%  
Percentage of non-operating working interest sold 40.00%              
Proceeds from sale of non-operating working interest 30,500,000              
Reversal of asset retirement obligation $ 4,000,000