Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans and Commitments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 27,325	$ 23,252
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend	72	71
Letter of Credit [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend	60	60
Unused lines of Credit [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend	12	11
Accrual Loans [Member] [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Troubled Debt Restructuring	6,697	8,512
Non Accrual Loans [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 20,628	$ 14,740