Annual report pursuant to Section 13 and 15(d)

Contingencies - Additional Information (Detail)

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Contingencies - Additional Information (Detail) (USD $)
 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2013
Jan. 31, 2014
Subsequent Event
Dec. 31, 2013
Cameron Parish Louisiana Claim
Dec. 31, 2012
Cameron Parish Louisiana Claim
Dec. 31, 2009
Royalties
Sep. 30, 2010
Royalties
Dec. 31, 2013
Contingent Liability Recorded
Dec. 31, 2012
Contingent Liability Recorded
Dec. 31, 2011
Contingent Liability Recorded
Dec. 31, 2013
Environmental Issue
Plea Agreement Fine
Dec. 31, 2013
Environmental Issue
Community Service Payment
Loss Contingencies [Line Items]                      
Plea agreement fine payment, which is subject to federal district court approval                   $ 700,000 $ 300,000
Claims paid     1,300,000 10,000,000              
Costs incurred related to an insurance claim in dispute 45,700,000                    
Costs anticipated to be incurred related to an insurance claim in dispute 1,900,000                    
Allowable reductions of cash payments         5,300,000            
Notified disallowed amount in reductions taken by ONRR           4,700,000          
Expenses related to accrued and settled claims             500,000 9,300,000 1,700,000    
Liability loss contingency             200,000 1,300,000      
Underpayment of royalties   $ 30,000