Effect of Master Netting Arrangements on Presentation of Derivative Assets and Liabilities in Consolidated Statements of Financial Condition (Parenthetical) (Detail) (Treasury Options, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Treasury Options
Derivatives, Fair Value [Line Items]
Gross Amounts Of Recognized Assets	$ 4,100	$ 2,600