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Basis of Presentation - (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Composition of assets held for sale:  
Assets held for sale $ 165,478
Composition of liabilities held for sale:  
Liabilities held for sale (8,346)
Oil and Gas Properties
 
Composition of assets held for sale:  
Assets held for sale 161,140
Transportation And Field
 
Composition of assets held for sale:  
Assets held for sale 3
Accounts Receivable
 
Composition of assets held for sale:  
Assets held for sale 4,117
Oil Inventory
 
Composition of assets held for sale:  
Assets held for sale 218
Accounts Payable
 
Composition of liabilities held for sale:  
Liabilities held for sale (354)
Asset Retirement Obligation Costs
 
Composition of liabilities held for sale:  
Liabilities held for sale (2,816)
Accrued Liabilities
 
Composition of liabilities held for sale:  
Liabilities held for sale $ (5,176)