Quarterly report pursuant to Section 13 or 15(d)

Contingencies - Additional Information (Details)

v2.4.0.8
Contingencies - Additional Information (Details) (USD $)
 1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jan. 31, 2014
Jun. 30, 2014
Mar. 31, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Dec. 31, 2009
Dec. 31, 2013
Sep. 30, 2010
Loss Contingencies [Line Items]                  
Under payment of royalties $ 30,000                
Under payment percentage of total royalty payments 0.0045%                
Statutory fine payment relative to underpayment     2,300,000            
Insurance claim expect to be recovered under the excess policies   46,300,000     46,300,000        
Reduction in royalties for transportation services             5,300,000    
Notified disallowed amount in reductions taken by ONRR                 4,700,000
Expenses related to claims, complaints and fines   400,000   100,000 300,000 100,000      
Liability loss contingency   $ 500,000     $ 500,000     $ 200,000