Non-performing Loans and Impaired Loans - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019 USD ($) ConsecutivePayment	Dec. 31, 2018 USD ($)
Financing Receivable, Modifications [Line Items]
Non-accrual loans	$ 14,764,000	$ 11,548,000
Non-performing TDRs	$ 1,600,000
Loan delinquency period	90 days
Minimum period required for satisfactory performance to return loan from non-accrual to accrual status	6 months
Restructured loan reported in TDRs	$ 3,800,000
Restructured loan returned to accruing status number of Consecutive Payments of loan | ConsecutivePayment	6
Specific reserves allocated to troubled debt restructuring	$ 20,000
Performing Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Restructured loan reported in TDRs	$ 2,200,000
Number TDRs returned to accrual status | ConsecutivePayment	0
Loans Purchased With Evidence of Credit Deterioration [Member]
Financing Receivable, Modifications [Line Items]
Non-accrual loans	$ 2,400,000
Non-performing TDRs	$ 640,000
Minimum [Member]
Financing Receivable, Modifications [Line Items]
Loan delinquency period	90 days
Delay or shortfall in payments of loan	30 days
Loans with an aggregate credit exposure	$ 1,000,000
Loans classified as TDR after a period	90 days
Minimum [Member] | Good Pass [Member]
Financing Receivable, Modifications [Line Items]
Number of consecutive years of profit Unaudited Financial Information for Good Pass Rating	5 years
Number of years of Satisfactory Relationship with bank for Good Pass Rating	5 years
Minimum [Member] | Satisfactory Pass [Member]
Financing Receivable, Modifications [Line Items]
Number of consecutive years of profit for Good Pass Rating	3 years
Maximum [Member]
Financing Receivable, Modifications [Line Items]
Loans with an aggregate credit exposure	$ 3,500,000
Loans classified as TDR after a period	120 days
Minimum number of years of Satisfactory Repayment required for Satisfactory Pass Rating	2 years