Quarterly report pursuant to Section 13 or 15(d)

Contingencies (Detail)

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Contingencies (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended 12 Months Ended
Sep. 30, 2010
Jun. 30, 2012
Dec. 31, 2009
Dec. 31, 2011
Estimated contingency reserve change   $ 8.4    
Liability loss contingency   10.4   2.0
Allowable reductions of cash payments     (5.3)  
Notified disallowed amount in reductions taken by ONRR $ 4.7