Derivative Financial Instruments (Detail) (Derivatives Designated as Hedges, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Asset derivatives fair value	$ 26,081	$ 2,831
Liability derivatives fair value	4,647	7,860
Accounts receivable-other
Derivative [Line Items]
Asset derivatives fair value	12,311	2,765
Other assets
Derivative [Line Items]
Asset derivatives fair value	13,770	66
Accounts payable
Derivative [Line Items]
Liability derivatives fair value	3,604	6,891
Other liabilities
Derivative [Line Items]
Liability derivatives fair value	$ 1,043	$ 969