Derivative Financial Instruments (Detail) (Derivatives Designated as Hedges, USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Asset Derivatives Fair Value	$ 10,244	$ 2,831
Liability Derivatives Fair Value	19,393	7,860
Accounts receivable-other
Derivative [Line Items]
Asset Derivatives Fair Value	7,506	2,765
Other assets
Derivative [Line Items]
Asset Derivatives Fair Value	2,738	66
Accounts payable
Derivative [Line Items]
Liability Derivatives Fair Value	11,073	6,891
Other liabilities
Derivative [Line Items]
Liability Derivatives Fair Value	$ 8,320	$ 969