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Partnership's Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, Derivatives Not Designated as Hedging Instruments under FASB ASC 815-10, Commodity Contract, USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Assets, commodity contracts $ 7,405 $ 15,100
Derivative Liabilities, commodity contracts (9,472) (10,549)
Fair asset and fair liability value of derivative instruments
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Assets, commodity contracts 7,405 15,100
Fair liability and fair asset value of derivative instruments
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Liabilities, commodity contracts (9,472) (10,549)
Quoted Prices in Active Markets for Identical Assets Level 1
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Assets, commodity contracts 1,270 1,749
Derivative Liabilities, commodity contracts (1,623) (1,898)
Quoted Prices in Active Markets for Identical Assets Level 1 | Fair asset and fair liability value of derivative instruments
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Assets, commodity contracts 1,270 1,749
Quoted Prices in Active Markets for Identical Assets Level 1 | Fair liability and fair asset value of derivative instruments
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Liabilities, commodity contracts (1,623) (1,898)
Significant Other Observable Inputs Level 2
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Assets, commodity contracts 6,135 13,351
Derivative Liabilities, commodity contracts (7,849) (8,651)
Significant Other Observable Inputs Level 2 | Fair asset and fair liability value of derivative instruments
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Assets, commodity contracts 6,135 13,351
Significant Other Observable Inputs Level 2 | Fair liability and fair asset value of derivative instruments
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative Liabilities, commodity contracts $ (7,849) $ (8,651)