Derivative Financial Instruments (Detail) (Derivatives Designated as Hedges, USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Asset derivatives fair value	$ 6,925	$ 26,081
Liability derivatives fair value	49,817	4,647
Accounts receivable-other
Derivative [Line Items]
Asset derivatives fair value	5,427	12,311
Other assets
Derivative [Line Items]
Asset derivatives fair value	1,498	13,770
Accounts payable
Derivative [Line Items]
Liability derivatives fair value	15,539	3,604
Other liabilities
Derivative [Line Items]
Liability derivatives fair value	$ 34,278	$ 1,043