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Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
gal
Mar. 31, 2012
gal
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Aggregated cash posted as collateral in normal course of business 0.6  
Hedging positions secured under credit facility 7.0  
Call Option
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 900,000 800,000
Put Option
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 3,700,000 3,600,000
Inventory
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 700,000 400,000
Swap Contract to Buy Heating Oil
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 5,000,000 5,200,000
Synthetic calls
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 45,400,000 42,300,000
Future Contract To Buy Heating Oil
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 48,500,000 34,500,000
Future Contract To Sell Heating Oil
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 54,300,000 37,500,000
Swap Contracts To Sell Heating Oil
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 3,000,000 3,900,000
Swap Contract To Buy Gasoline
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 500,000 800,000
Swap Contract To Buy Diesel
    
Derivative Instruments and Hedging Activities Disclosure [Line Items]    
Derivative activity volume 300,000 400,000