Assets and Liabilities Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) (Quoted Prices in Active Markets for Identical Assets (Level 1), Treasury Options, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Quoted Prices in Active Markets for Identical Assets (Level 1) | Treasury Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets-other	$ 4,100	$ 2,600