Annual report pursuant to Section 13 and 15(d)

Purchase Price Allocation for Acquisition of Properties (Detail)

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Purchase Price Allocation for Acquisition of Properties (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Aug. 10, 2011
Fairway Properties
Oct. 05, 2012
Newfield Properties
May 11, 2011
Yellow Rose Properties
Apr. 30, 2010
Total Properties
Nov. 04, 2010
Tahoe Properties
Business Acquisition [Line Items]              
Oil and natural gas properties and equipment     $ 50,682 $ 237,214 $ 396,902 $ 121,301 $ 134,189
Asset retirement obligations - current (92,630) (138,185)   (7,250)      
Asset retirement obligations - non-current (291,423) (255,695) (7,812) (24,414) (382) (6,289) (17,956)
Long-term liability         (2,143)    
Total cash paid     $ 42,870 $ 205,550 $ 394,377 $ 115,012 $ 116,233