Loans - Loans Individually Evaluated for Impairment Including Loans Modified in Troubled Debt Restructurings by Portfolio Segment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
With an allowance recorded:
Allowance for Loan Losses Allocated	$ 2,301	$ 4,722
With no related allowance recorded:
Unpaid Principal Balance, Total	24,431	23,707
Recorded Investment, Total	20,755	17,918
Commercial, industrial, and agricultural
With an allowance recorded:
Unpaid Principal Balance	2,657	3,053
Recorded Investment	1,476	3,037
Allowance for Loan Losses Allocated	673	158
With no related allowance recorded:
Unpaid Principal Balance	9,845	3,684
Recorded Investment	9,695	2,874
Commercial mortgages
With an allowance recorded:
Unpaid Principal Balance	6,541	10,799
Recorded Investment	4,349	6,709
Allowance for Loan Losses Allocated	1,594	4,454
With no related allowance recorded:
Unpaid Principal Balance	4,903	5,659
Recorded Investment	4,770	4,786
Residential real estate
With an allowance recorded:
Unpaid Principal Balance	485	502
Recorded Investment	465	502
Allowance for Loan Losses Allocated	34	100
With no related allowance recorded:
Unpaid Principal Balance	0	0
Recorded Investment	$ 0	0
Overdrafts
With an allowance recorded:
Unpaid Principal Balance		10
Recorded Investment		10
Allowance for Loan Losses Allocated		$ 10

Impaired Financing Receivable, Unpaid Principal Balance With No Allowance Recorded [Abstract]

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- Definition

Impaired Financing Receivable, Unpaid Principal Balance With an Allowance Recorded [Abstract]

+ References

No definition available.

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- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953550-111524

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

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Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

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Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

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- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

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Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

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- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

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