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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Total	$ 22,330	$ 26,424	$ 22,434	$ 24,827
Interest Income Recognized, Total	4	6	11	17
Cash Basis Interest Recognized, Total	4	6	11	17
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	1,267	4,140	1,439	3,406
Interest Income Recognized, Related Allowance	3	0	4	3
Cash Basis Interest Recognized, Related Allowance	3	0	4	3
Average Recorded Investment, No Related Allowance	2,055	3,506	2,121	3,459
Interest Income Recognized, No Related Allowance	0	0	0	0
Cash Basis Interest Recognized, No Related Allowance	0	0	0	0
Commercial Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	8,337	6,180	7,657	5,549
Interest Income Recognized, Related Allowance	0	3	3	3
Cash Basis Interest Recognized, Related Allowance	0	3	3	3
Average Recorded Investment, No Related Allowance	10,602	11,971	10,888	12,016
Interest Income Recognized, No Related Allowance	0	0	0	0
Cash Basis Interest Recognized, No Related Allowance	0	0	0	0
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	0	476	191	322
Interest Income Recognized, Related Allowance	1	3	4	11
Cash Basis Interest Recognized, Related Allowance	1	3	4	11
Average Recorded Investment, No Related Allowance	69	151	138	75
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=28368275&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=28368275&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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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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