Carrying Value of Assets and Liabilities Recorded at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Commodity derivative contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	$ 18,800
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	3,411	1,970
Derivative liabilities	34,760	14,305
Fair Value, Measurements, Recurring [Member] | Commodity derivative contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	1,970
Derivative liabilities	21,367	0
Fair Value, Measurements, Recurring [Member] | Nonqualified employee savings plans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	13,393	13,267
Fair Value, Measurements, Recurring [Member] | Foreign exchange derivative contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	3,411	0
Derivative liabilities	0	1,038
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	13,393	13,267
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Commodity derivative contracts [Member]
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) [Member] | Fair Value, Measurements, Recurring [Member] | Nonqualified employee savings plans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	13,393	13,267
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Foreign exchange derivative contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	3,411	1,970
Derivative liabilities	21,367	1,038
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Commodity derivative contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	1,970
Derivative liabilities	21,367	0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Nonqualified employee savings plans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Foreign exchange derivative contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	3,411	0
Derivative liabilities	0	1,038
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Commodity derivative contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Nonqualified employee savings plans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Foreign exchange derivative contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	$ 0	$ 0