Loans and Allowance for Credit Losses - Troubled Debt Restructuring is 90 Days or More Past Due (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) Contract	Mar. 31, 2020 USD ($) Contract
Financing Receivable, Past Due [Line Items]
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts | Contract	0	1
Financing Receivable, Troubled Debt Restructuring, Subsequent Default | $	$ 0	$ 71
Residential real estate [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts | Contract	0	1
Financing Receivable, Troubled Debt Restructuring, Subsequent Default | $	$ 0	$ 71