Activity in Valuation Allowance for Mortgage Servicing Right (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Valuation Allowance [Line Items]
Balance, beginning of year	$ 475	$ 325	$ 500
Additions	190	355
Reductions		(205)	(175)
Balance, end of year	$ 665	$ 475	$ 325