Quarterly report pursuant to Section 13 or 15(d)

Contingencies - Additional Information (Details)

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Contingencies - Additional Information (Details)
 1 Months Ended 3 Months Ended 6 Months Ended
Jan. 31, 2014
USD ($)
Mar. 31, 2014
USD ($)
Jun. 30, 2015
USD ($)
claim
Dec. 15, 2014
USD ($)
Dec. 31, 2010
USD ($)
Loss Contingencies [Line Items]          
Underpayment of royalties $ 30,000        
Under payment percentage of total royalty payments 0.0045%        
Statutory fine payment relative to underpayment   $ 2,300,000      
Loss contingency, range of possible loss, minimum       $ 0  
Loss contingency, range of possible loss, maximum       $ 32,000,000  
Insurance claims submitted for removal-of-wreck expenses     $ 42,000,000    
Notified disallowed amount in reductions taken by ONRR         $ 4,700,000
BSEE          
Loss Contingencies [Line Items]          
Number of notices received form BSEE | claim     2    
Proposed civil penalties related to various incidents of noncompliance, total     $ 3,600,000    
Civil penalties related liability     0    
Liberty Mutual Insurance Co          
Loss Contingencies [Line Items]          
Insurance claims received     5,000,000    
Revised estimate          
Loss Contingencies [Line Items]          
Insurance claims receivable     30,000,000    
Comprehensive General Liability policy          
Loss Contingencies [Line Items]          
Insurance claims received     1,000,000    
Energy Package          
Loss Contingencies [Line Items]          
Insurance claims received     1,000,000    
Starr Marine          
Loss Contingencies [Line Items]          
Insurance claims received     $ 5,000,000