Assets and Liabilities Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) (Treasury Options, Quoted Prices in Active Markets for Identical Assets (Level 1), USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Treasury Options | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets-other	$ 1,300	$ 5,300