Fair Value Measurement of Assets and Liabilities - Changes in Level 3 Assets Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers from held-to-maturity	$ 18,300