Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans and Commitments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Abstract]
Accrual status	$ 7,542	$ 8,757	$ 11,563
Nonaccrual status	6,037	11,761	11,222
Total	13,579	20,518	22,785
Letters of Credit Outstanding, Amount	60	60	60
Unused lines of credit	$ 163	$ 1,027	$ 54