Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) SecurityLoan	Jun. 30, 2019 USD ($) SecurityLoan	Jun. 30, 2020 USD ($) SecurityLoan	Jun. 30, 2019 USD ($) SecurityLoan	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for calculating Loss migration rates of portfolio segments			3 years
Allowance for loan losses	$ 20,420,000		$ 20,420,000		$ 14,767,000
Provision for loan losses	3,486,000		$ 5,612,000
Number of days past due for loans to be considered as nonperforming			90 days
Reasonable period for nonperforming TDRs to be returned to performing status			6 months
Number of days reaching where loans are considered for nonaccrual status			90 days
Conditions where loans are considered for nonaccrual status			A loan may be returned to accruing status only if one of three conditions are met: the loan is well-secured and none of the principal and interest has been past due for a minimum of 90 days; the loan is a TDR and has made a minimum of six months payments; or the principal and interest payments are reasonably assured and a sustained period of performance has occurred, generally six months.
Loans modified as troubled debt restructuring	$ 0	$ 0	$ 0	$ 0
Defaulted loans | SecurityLoan	0	0	0	0
Impaired loans			greater than $350
Allowance for loan losses recorded for acquired loans			$ 0		0
Foreclosed assets	$ 0		0		0
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential mortgages in process of foreclosure	867,000		867,000		1,022,000
TDRs [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 92,000		$ 92,000		$ 91,000