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Derivative Instruments - Outstanding Trading Contracts (Detail) (Forward Contracts [Member], USD $) | Dec. 31, 2012 gal
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Revenue [Member] |
Derivative [Line Items] |
Quantity in Gallons | 1,262,000
Weighted Average Contract Prices | $ 0.9214
Purchase [Member] |
Derivative [Line Items] |
Quantity in Gallons | 2,648,000
Weighted Average Contract Prices | $ 0.9291
Minimum [Member] | Revenue [Member] |
Derivative [Line Items] |
Estimated Market Prices | $ 0.7550
Minimum [Member] | Purchase [Member] |
Derivative [Line Items] |
Estimated Market Prices | $ 0.7550
Maximum [Member] | Revenue [Member] |
Derivative [Line Items] |
Estimated Market Prices | $ 1.3650
Maximum [Member] | Purchase [Member] |
Derivative [Line Items] |
Estimated Market Prices | $ 1.3300

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- Details
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