Loans - Additional Information (Detail)	12 Months Ended
Dec. 31, 2016 USD ($) Loans	Dec. 31, 2015 USD ($) Loans	Dec. 31, 2014 USD ($) Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net unamortized loan (fees) costs	$ (1,507,000)	$ (636,000)
Percentage of comprised loan, commercial, industrial and agricultural loans	30.00%	30.00%
Percentage of comprised loan, commercial mortgage loans	31.00%	28.00%
Percentage of loan-to-value to business equipment	80.00%
Percentage of loan-to-value to accounts receivable	75.00%
Percentage of loan-to-value to business inventory	60.00%
Percentage of loan-to-value to real estate	85.00%
Percentage of residential real estate loan in portfolio	35.00%	36.00%
Additional provision for loan losses	$ 0	$ 0	$ 319,000
Minimum period to be considered for loan to have defaulted	90 days
Principal balances forgiven in connection with loan restructuring	$ 0	0
Loans modified in a troubled debt restructuring	$ 11,831,000	$ 14,941,000
Number of Loans \| Loans	15	16
Charge-offs	$ 4,961,000	$ 3,718,000	$ 3,182,000
Outstanding balance of semi annual loans	Greater than $1 million
Outstanding balance of annual loans	Less than $1 million
Trouble Debt Restructuring [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| Loans	1	1	4
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of consumer loan and credit card in portfolio	10.00%	10.00%
Reduction in stated interest rate modification having loan range period	15 years
Extension of maturity date modification having loan range period	18 years
Minimum [Member]
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, Industrial, and Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in a troubled debt restructuring	$ 2,640,000	$ 5,040,000
Number of Loans \| Loans	7	8
Charge-offs	$ 601,000	$ 307,000	$ 618,000
Commercial, Industrial, and Agricultural [Member] \| Trouble Debt Restructuring [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in a troubled debt restructuring			$ 2,315,000
Number of Loans \| Loans	1	1	1
Additional provision for loan losses			$ 48,000
Charge-offs			0
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in a troubled debt restructuring	$ 9,191,000	$ 9,901,000
Number of Loans \| Loans	8	8
Charge-offs	$ 201,000	$ 486,000	50,000
Commercial Mortgages [Member] \| Trouble Debt Restructuring [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in a troubled debt restructuring			$ 4,879,000
Number of Loans \| Loans	0	0	3
Additional provision for loan losses			$ 271,000
Commercial and Industrial [Member] \| Trouble Debt Restructuring [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in a troubled debt restructuring	$ 109,000	$ 1,327,000
Number of Loans \| Loans	1	1
Additional provision for loan losses	$ 0	$ 0
Charge-offs	$ 0	$ 0

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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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Outstanding balance of annual loans.

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Outstanding balance of semi annual loans.

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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
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Amount of direct write-downs of financing receivables charged against the allowance.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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