Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans and Commitments (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 13,031	$ 13,579
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend	273	223
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	213	163
Accrual Loans [Member] [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Troubled Debt Restructuring	7,509	7,542
Non Accrual Loans [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 5,522	$ 6,037