Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	$ 12,562	$ 13,425
Balance at period end	9,285	11,805
Commercial Portfolio Segment [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	3,660	3,845
Balance at period end	1,415	2,188
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	6,606	9,456
Balance at period end	6,585	9,494
Construction Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	1,192	0
Balance at period end	1,181	0
Total consumer real estate loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	0	124
Balance at period end	0	123
Consumer Loan [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at time of restructuring	1,104	0
Balance at period end	$ 104	$ 0