Loans - Impaired Financing Receivables with Related and not Related Allowances (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Total	$ 18,310	$ 22,330	$ 18,146	$ 22,434
Interest Income Recognized, Total	179	4	192	11
Cash Basis Interest Recognized, Total	179	4	192	11
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	4,023	1,267	4,342	1,439
Interest Income Recognized, Related Allowance	62	3	64	4
Cash Basis Interest Recognized, Related Allowance	62	3	64	4
Average Recorded Investment, No Related Allowance	2,012	2,055	2,071	2,121
Interest Income Recognized, No Related Allowance	32	0	32	0
Cash Basis Interest Recognized, No Related Allowance	32	0	32	0
Commercial Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	5,511	8,337	5,415	7,657
Interest Income Recognized, Related Allowance	18	0	18	3
Cash Basis Interest Recognized, Related Allowance	18	0	18	3
Average Recorded Investment, No Related Allowance	6,288	10,602	6,080	10,888
Interest Income Recognized, No Related Allowance	22	0	22	0
Cash Basis Interest Recognized, No Related Allowance	22	0	22	0
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	400	0	200	191
Interest Income Recognized, Related Allowance	45	1	56	4
Cash Basis Interest Recognized, Related Allowance	45	1	56	4
Average Recorded Investment, No Related Allowance	76	69	38	138
Interest Income Recognized, No Related Allowance	0	0	0	0
Cash Basis Interest Recognized, No Related Allowance	$ 0	$ 0	$ 0	$ 0

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Average 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 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5258-111524

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- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

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Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

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- Definition

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

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

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Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

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

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Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

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Amount of interest income on financing receivables, for which there is a related allowance for credit losses, recognized on a cash-basis method of accounting that the financing receivables were impaired.

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