Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 13,492	$ 11,961
Assets, Fair Value, Total	62,346	59,681
Liabilities, Fair Value, Total	(1,679)	(11,937)
Hedging contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	48,854	47,720
Derivative Liabilities, Fair Value	(1,679)	(11,937)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	13,492	11,961
Assets, Fair Value, Total	13,492	11,961
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value, Total	48,854	47,720
Liabilities, Fair Value, Total	(1,679)	(11,937)
Significant Other Observable Inputs (Level 2) | Hedging contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, Fair Value	48,854	47,720
Derivative Liabilities, Fair Value	$ (1,679)	$ (11,937)