Allowance for Loan and Lease Losses and Credit Quality Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) SecurityLoan loan	Dec. 31, 2018 USD ($) SecurityLoan loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income on impaired loans	$ 800,000	$ 800,000
Troubled debt restructuring related reserves	$ 600,000	$ 1,200,000
Number of TDRs | loan	4	5
Subsequent default, loan amount	$ 300,000	$ 200,000
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease in allowance for loan losses	200,000	2,000,000.0
Troubled debt restructurings charged off	$ 0	$ 5,000,000.0
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans in the process of foreclosure | SecurityLoan	33	26
Mortgage loans, foreclosures	$ 3,200,000	$ 1,900,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans in the process of foreclosure | SecurityLoan	29	11
Mortgage loans, foreclosures	$ 9,500,000	$ 5,300,000