Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans and Commitments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Abstract]
Accrual status	$ 8,512	$ 7,542	$ 8,757
Nonaccrual status	14,740	6,037	11,761
Total	23,252	13,579	20,518
Letters of Credit Outstanding, Amount	60	60	60
Unused lines of credit	11	163	1,027
Commitments Net	$ 71	$ 223	$ 1,087