Investment Securities - Summary of Transfers between Level 1 and Level 2 (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Transfers from Level 2 to Level 1	$ 15,751	$ 7,135
Corporate Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Transfers from Level 2 to Level 1	13,941	4,598
Foreign Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Transfers from Level 2 to Level 1	$ 1,810	$ 2,537