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Reconciliation of The Provision For Incom Taxes (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Provision For Income Taxes Reconciliation [Line Items]    
Statutory tax rate 34.00% 34.00%
Derivative instruments (94.80%) 7.80%
Oil costs and long-lived assets 30.70% (0.30%)
Non-deductible expenses 14.90% (5.10%)
Change in valuation allowance 15.20% (36.40%)
Effective tax rate 0.00% 0.00%