Carrying Value of Assets and Liabilities Recorded at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	$ 13,108	$ 197
Derivative liabilities	(12,482)	(42,905)
Commodity derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	9,496	197
Derivative liabilities	(3,176)	(489)
Foreign exchange derivative contract
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	3,612	0
Derivative liabilities	0	(8,459)
Nonqualified employee savings plans
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	(9,306)	(8,030)
Interest rate derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	0	(25,927)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	(9,306)	(8,030)
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign exchange derivative contract
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Nonqualified employee savings plans
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	(9,306)	(8,030)
Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	13,108	197
Derivative liabilities	(3,176)	(34,875)
Significant Other Observable Inputs (Level 2) | Commodity derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	9,496	197
Derivative liabilities	(3,176)	(489)
Significant Other Observable Inputs (Level 2) | Foreign exchange derivative contract
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	3,612	0
Derivative liabilities	0	(8,459)
Significant Other Observable Inputs (Level 2) | Nonqualified employee savings plans
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	0	0
Significant Other Observable Inputs (Level 2) | Interest rate derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	0	(25,927)
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) | Commodity derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) | Foreign exchange derivative contract
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) | Nonqualified employee savings plans
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) | Interest rate derivative contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	$ 0	$ 0