Gains and Losses on Derivative Instruments Recognized in Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives, ineffectiveness and the time component on fair value hedging instruments	$ (9,695)	$ (5,830)
Hedge Ineffectiveness | Cost of product sales and natural gas storage services
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives, ineffectiveness and the time component on fair value hedging instruments	(500)	9,746
Time Value | Cost of product sales and natural gas storage services
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives, ineffectiveness and the time component on fair value hedging instruments	(9,195)	(15,576)
Derivatives NOT Designated as Hedging Instruments | Physical Fixed Price Derivative Contracts | Product sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	5,141	3,032
Derivatives NOT Designated as Hedging Instruments | Physical Fixed Price Derivative Contracts | Cost of product sales and natural gas storage services
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	5,968
Derivatives NOT Designated as Hedging Instruments | Physical Index Derivative Contracts | Product sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	123
Derivatives NOT Designated as Hedging Instruments | Physical Index Derivative Contracts | Cost of product sales and natural gas storage services
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	98
Derivatives NOT Designated as Hedging Instruments | Futures Contracts | Refined Products | Cost of product sales and natural gas storage services
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	7,103	22,073
Derivatives Designated as Hedging Instruments | Futures Contracts | Refined Products | Cost of product sales and natural gas storage services
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(47,681)	(61,235)
Derivatives Designated as Hedging Instruments | Physical Inventory | Cost of product sales and natural gas storage services
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ 37,986	$ 55,405