Impaired Loans (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Impaired Loans:
Impaired loans without a valuation allowance	$ 6,322	$ 4,702
Impaired loans with a valuation allowance	4,510	4,858
Total impaired loans	10,832	9,560
Allowance for loan losses on impaired loans at period End	1,028	968
Total nonaccrual loans	7,949	6,056
Past due 90 days or more and still accruing	6	669
Average investment in impaired loans	$ 9,534	$ 7,077