Changes in Other Real Estate Owned (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Real Estate Properties [Line Items]
Balance at beginning of period	$ 615	$ 1,829	$ 1,829
Properties acquired at foreclosure	1,161		2,305
Sales of foreclosed properties			(2,892)
Valuation adjustments	(166)	(204)	(627)
Balance at end of period	$ 1,610		$ 615