Loans - Additional Information (Detail)	12 Months Ended
Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net unamortized loan fees	$ 3,175,000	$ 3,157,000
Percentage of comprised loan, commercial, industrial and agricultural loans	37.00%	33.00%
Percentage of comprised loan, commercial mortgage loans	28.00%	30.00%
Percentage of loan-to-value to business equipment (up to)	80.00%
Percentage of loan-to-value to accounts receivable (up to)	75.00%
Percentage of loan-to-value to business inventory (up to)	60.00%
Percentage of loan-to-value to real estate (up to)	85.00%
Percentage of residential real estate loan in portfolio	31.00%	33.00%
Allowance for loan losses, period increase (decrease)	$ 351,000	$ 4,024,000	$ 0
Minimum period to be considered for loan to have defaulted	90 days
Principal balances forgiven in connection with loan restructuring	$ 0	$ 0
Number of loans \| loan	25	20
Modified in a troubled debt restructuring	$ 14,626,000	$ 17,303,000
Charge-offs	$ 6,593,000	$ 4,077,000	$ 4,961,000
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of consumer loan and credit card in portfolio	4.00%	4.00%
Reduction in stated interest rate modification having loan range period	18 years
Extension of maturity date modification having loan range period	18 years
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reduction in stated interest rate modification having loan range period	4 years
Extension of maturity date modification having loan range period	4 years
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans \| loan		4	1
Modified in a troubled debt restructuring		$ 2,750,000	$ 109,000
Charge-offs		$ 0	$ 0
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans \| loan	5	2
Modified in a troubled debt restructuring	$ 1,677,000	$ 6,421,000
Additional provision for loan losses	351,000	3,895,000
Charge-offs	$ 0	$ 0
Troubled Debt Restructuring, Debtor, Prior Period \| Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans \| loan	1
Additional provision for loan losses	$ 1,847,000
Charge-offs	$ 3,336,000

Additional provision for loan losses.

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Commercial industrial and agricultural loan amount as maximum percentage of accounts receivable.

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Commercial industrial and agricultural loan amount as maximum percentage of business equipment.

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Commercial industrial and agricultural loan amount as maximum percentage of business inventory.

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Commercial mortgage loan amount as maximum percentage of appraised real estate value.

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Minimum period to be considered for loan to have defaulted.

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Modification involving extension of maturity date having loan period.

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Modification involving reduction of stated interest rate having loan period.

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Percentage of commercial industrial and agricultural loans in loan portfolio.

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Percentage of commercial mortgage loans in loan portfolio.

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Percentage of consumer loans and credit card products in loan portfolio.

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Percentage of residential real estate loans in loan portfolio.

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Troubled debt restructuring loan principal balance forgiven.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of increase (decrease) of allowance reserve for credit loss.

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Amount of direct write-downs of financing receivables charged against the allowance.

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Number of financing receivables that have been modified by troubled debt restructurings.

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The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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