CREDIT QUALITY ASSESSMENT - Restructured Loans at the date of Restructuring For Specific Segments of the Loan Portfolio (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance	$ 13,477	$ 4,533
Individual allowance	214	1,020
Restructured and subsequently defaulted	0	0
All Other Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance	0	549
Individual allowance	0	0
Restructured and subsequently defaulted	0	0
Troubled debt restructurings:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured accruing	0	929
Restructured non-accruing	13,477	3,604
Troubled debt restructurings: | All Other Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured accruing	0	549
Restructured non-accruing	0	0
Commercial real estate: | Commercial investor real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance	9,594	723
Individual allowance	0	65
Restructured and subsequently defaulted	0	0
Commercial real estate: | Commercial owner-occupied real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance	3,157	930
Individual allowance	0	0
Restructured and subsequently defaulted	0	0
Commercial real estate: | Commercial AD&C
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance	0	0
Individual allowance	0	0
Restructured and subsequently defaulted	0	0
Commercial real estate: | Troubled debt restructurings: | Commercial investor real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured accruing	0	0
Restructured non-accruing	9,594	723
Commercial real estate: | Troubled debt restructurings: | Commercial owner-occupied real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured accruing	0	0
Restructured non-accruing	3,157	930
Commercial real estate: | Troubled debt restructurings: | Commercial AD&C
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured accruing	0	0
Restructured non-accruing	0	0
Commercial Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance	726	2,331
Individual allowance	214	955
Restructured and subsequently defaulted	0	0
Commercial Business | Troubled debt restructurings:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Restructured accruing	0	380
Restructured non-accruing	$ 726	$ 1,951