Securities Available-for-Sale - Schedule of Roll-Forward Amount of Credit-Related OTTI (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables [Line Items]
Balance, beginning of period	$ 204	$ 226
OTTI credit loss recorded		10	226
OTTI reduction from sale or maturity		(32)
Balance, end of period	$ 204	$ 204	$ 226