XML 16 R78.htm IDEA: XBRL DOCUMENT v2.4.0.6
Asset Retirement Obligations - Reconciliation of Beginning and Ending Aggregate Carrying Amounts of Asset Retirement Obligation (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Asset retirement obligations, beginning balance $ 498,410    
Liability incurred upon acquiring and drilling wells 1,102 1,377  
Liability settled or disposed in current period (50,722)    
Accretion 9,779 2,607  
Asset retirement obligations, ending balance 458,569    
Less: current portion 91,113   118,504
Asset retirement obligations, net of current $ 367,456   $ 379,906