Categories of Loan (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Accounts Notes And Loans Receivable [Line Items]
Commercial loans	$ 61,721		$ 52,286
Commercial real estate	163,222		158,314
Residential real estate	83,200		83,870
Installment loans	18,182		21,284
Total gross loans	326,325		315,754
Less allowance for loan losses	(2,727)	$ (2,697)	(2,400)	$ (3,024)	$ (3,132)	$ (2,894)
Total loans	$ 323,598		$ 313,354