Investment Securities - Summary of Transfers between Level 1 and Level 2 (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 1 to Level 2
Transfers from Level 2 to Level 1	10,137	17,746
Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 1 to Level 2
Transfers from Level 2 to Level 1	8,585	16,745
Foreign corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 1 to Level 2
Transfers from Level 2 to Level 1	$ 1,552	$ 1,001