Loans - Recorded Investment in Nonaccrual Loans by Portfolio Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	$ 1,188	$ 542	$ 900
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	1,071	462
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	70	72
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in nonaccrual loans	$ 47	$ 8