Derivative Financial Instruments (Detail) (Derivatives Designated as Hedges, USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Asset derivatives fair value	$ 12,619	$ 26,081
Liability derivatives fair value	30,188	4,647
Accounts receivable-other
Derivative [Line Items]
Asset derivatives fair value	11,270	12,311
Accounts payable
Derivative [Line Items]
Liability derivatives fair value	13,145	3,604
Other assets
Derivative [Line Items]
Asset derivatives fair value	1,349	13,770
Other liabilities
Derivative [Line Items]
Liability derivatives fair value	$ 17,043	$ 1,043