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Fair Value of Financial Instruments (Narrative) (Detail) - $ / gal
Dec. 31, 2015
Dec. 31, 2014
Fair Value of Financial Instruments [Abstract]    
Minimum range of DOE index curve used in DCF model 2.21 2.96
Maximum range of DOE index curve used in DCF model 2.64 3.41
Weighted average DOE index curve used in DCF model 2.43 3.04