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Derivative Activities - Schedule of Additional Information Related to Master Netting Arrangements with Derivative Counterparties (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Derivative [Line Items]    
Gross Amounts of Recognized Assets $ 33,360 $ 165,076
Gross Amounts Offset in the Balance Sheet (19,706) (11,809)
Net Amounts of Assets Presented in the Balance Sheet 13,654 153,267
Gross Amounts of Recognized (Liabilities) (45,929) (19,743)
Gross Amounts Offset in the Balance Sheet 19,706 11,809
Net Amounts of (Liabilities) Presented in the Balance Sheet (26,223) (7,934)
Natural gas | Swaps
    
Derivative [Line Items]    
Gross Amounts of Recognized Assets 4,240 10,746
Gross Amounts Offset in the Balance Sheet (1,218) (3,242)
Net Amounts of Assets Presented in the Balance Sheet 3,022 7,504
Gross Amounts of Recognized (Liabilities) (4,790) (3,242)
Gross Amounts Offset in the Balance Sheet 1,218 3,242
Net Amounts of (Liabilities) Presented in the Balance Sheet (3,572)  
Natural gas | Collars
    
Derivative [Line Items]    
Gross Amounts of Recognized Assets 16,057 128,410
Gross Amounts Offset in the Balance Sheet (7,671) (6,155)
Net Amounts of Assets Presented in the Balance Sheet 8,386 122,255
Gross Amounts of Recognized (Liabilities) (13,345) (9,618)
Gross Amounts Offset in the Balance Sheet 7,671 6,155
Net Amounts of (Liabilities) Presented in the Balance Sheet (5,674) (3,463)
Natural gas | Basis Swap
    
Derivative [Line Items]    
Gross Amounts of Recognized Assets 7,686 993
Gross Amounts Offset in the Balance Sheet (7,686)  
Net Amounts of Assets Presented in the Balance Sheet   993
Gross Amounts of Recognized (Liabilities) (3,756)  
Gross Amounts Offset in the Balance Sheet 7,686  
Net Amounts of (Liabilities) Presented in the Balance Sheet 3,930  
Crude oil | Swaps
    
Derivative [Line Items]    
Gross Amounts of Recognized Assets 3,567 9,650
Gross Amounts Offset in the Balance Sheet (1,321)  
Net Amounts of Assets Presented in the Balance Sheet 2,246 9,650
Gross Amounts of Recognized (Liabilities) (4,711)  
Gross Amounts Offset in the Balance Sheet 1,321  
Net Amounts of (Liabilities) Presented in the Balance Sheet (3,390)  
Crude oil | Collars
    
Derivative [Line Items]    
Gross Amounts of Recognized Assets   2,222
Net Amounts of Assets Presented in the Balance Sheet   2,222
Gross Amounts of Recognized (Liabilities) (398)  
Net Amounts of (Liabilities) Presented in the Balance Sheet (398)  
Swap NGLs (Natural Gasoline) | C3 swaps
    
Derivative [Line Items]    
Gross Amounts of Recognized Assets 826  
Gross Amounts Offset in the Balance Sheet (826)  
Gross Amounts of Recognized (Liabilities) (18,172) (6,746)
Gross Amounts Offset in the Balance Sheet 826  
Net Amounts of (Liabilities) Presented in the Balance Sheet (17,346) (6,746)
Swap NGLs (Natural Gasoline) | C4 swaps
    
Derivative [Line Items]    
Gross Amounts of Recognized Assets 863  
Gross Amounts Offset in the Balance Sheet (863)  
Gross Amounts of Recognized (Liabilities) (757)  
Gross Amounts Offset in the Balance Sheet 863  
Net Amounts of (Liabilities) Presented in the Balance Sheet 106  
Swap NGLs (Natural Gasoline) | C5 swaps
    
Derivative [Line Items]    
Gross Amounts of Recognized Assets 121 13,055
Gross Amounts Offset in the Balance Sheet (121) (2,412)
Net Amounts of Assets Presented in the Balance Sheet   10,643
Gross Amounts of Recognized (Liabilities)   (137)
Gross Amounts Offset in the Balance Sheet 121 2,412
Net Amounts of (Liabilities) Presented in the Balance Sheet $ 121 $ 2,275