Loans - Loans Individually Evaluated for Impairment Including Loans Modified in Troubled Debt Restructurings by Portfolio Segment (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance, Total	$ 18,501	$ 24,657
Recorded Investment, Total	16,778	23,203
Allowance for Loan Losses Allocated	3,190	3,415
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance, Related Allowance	3,448	5,737
Recorded Investment, Related Allowance	3,448	5,737
Allowance for Loan Losses Allocated	1,126	411
Unpaid Principal Balance, No Related Allowance	3,716	2,530
Recorded Investment, No Related Allowance	2,788	1,577
Allowance for Loan Losses Allocated, No Related Allowance	0	0
Commercial Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance, Related Allowance	5,985	10,651
Recorded Investment, Related Allowance	5,343	10,212
Allowance for Loan Losses Allocated	2,025	2,807
Unpaid Principal Balance, No Related Allowance	5,001	5,020
Recorded Investment, No Related Allowance	4,951	5,020
Allowance for Loan Losses Allocated, No Related Allowance	0	0
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance, Related Allowance	351	400
Recorded Investment, Related Allowance	248	400
Allowance for Loan Losses Allocated	39	197
Unpaid Principal Balance, No Related Allowance	0	319
Recorded Investment, No Related Allowance	0	257
Allowance for Loan Losses Allocated, No Related Allowance	$ 0	$ 0

Impaired loans without allowance.

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+ 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953550-111524

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=49124121&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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=49124121&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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

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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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

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