Derivatives - Open Commodity Derivative Contracts (Detail) bbl in Thousands	9 Months Ended
	Sep. 30, 2015 bbl
Derivative [Line Items]
Derivative contract expiration date	Dec. 31, 2015
Crude Oil Exchange-Traded
Derivative [Line Items]
Percentage of derivative contracts expiring in the period	100.00%
Crude Oil Exchange-Traded | Long
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	12,123	[1]
Crude Oil Exchange-Traded | Short
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	22,751	[1]
Refined Products Exchange-Traded
Derivative [Line Items]
Percentage of derivative contracts expiring in the period	100.00%
Refined Products Exchange-Traded | Long
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	4,286	[1]
Refined Products Exchange-Traded | Short
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	1,921	[1]

[1] 100 percent of these contracts expire in the fourth quarter of 2015.