Annual report pursuant to Section 13 and 15(d)

Schedule of Derivative Assets at Fair Value (Detail)

v2.4.0.6
Schedule of Derivative Assets at Fair Value (Detail) (Swaps Oil, USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
bbl
Derivatives, Fair Value [Line Items]  
Notional Quantity (Bbls) 1,969,800
Weighted Average Contract Price 100.40
Fair Value Liability $ 9,401
2013: 1st quarter
 
Derivatives, Fair Value [Line Items]  
Termination Period 1st quarter
Notional Quantity (Bbls) 351,000
Weighted Average Contract Price 101.97
Fair Value Liability 2,566
2013: 2nd Quarter
 
Derivatives, Fair Value [Line Items]  
Termination Period 2nd quarter
Notional Quantity (Bbls) 336,700
Weighted Average Contract Price 101.97
Fair Value Liability 1,843
2013: 3rd Quarter
 
Derivatives, Fair Value [Line Items]  
Termination Period 3rd quarter
Notional Quantity (Bbls) 312,800
Weighted Average Contract Price 101.98
Fair Value Liability 1,205
2013: 4th Quarter
 
Derivatives, Fair Value [Line Items]  
Termination Period 4th quarter
Notional Quantity (Bbls) 294,400
Weighted Average Contract Price 101.98
Fair Value Liability 741
2014: 1st Quarter
 
Derivatives, Fair Value [Line Items]  
Termination Period 1st quarter
Notional Quantity (Bbls) 180,000
Weighted Average Contract Price 97.38
Fair Value Liability 1,085
2014: 2nd Quarter
 
Derivatives, Fair Value [Line Items]  
Termination Period 2nd quarter
Notional Quantity (Bbls) 172,900
Weighted Average Contract Price 97.38
Fair Value Liability 863
2014: 3rd Quarter
 
Derivatives, Fair Value [Line Items]  
Termination Period 3rd quarter
Notional Quantity (Bbls) 165,600
Weighted Average Contract Price 97.38
Fair Value Liability 647
2014: 4th Quarter
 
Derivatives, Fair Value [Line Items]  
Termination Period 4th quarter
Notional Quantity (Bbls) 156,400
Weighted Average Contract Price 97.37
Fair Value Liability $ 451