Loans - Impaired Financing Receivables with Related and not Related Allowances (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Total	$ 23,401	$ 19,079
Interest Income Recognized, Total	49	9
Cash Basis Interest Recognized, Total	49	9
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	5,981	4,660
Interest Income Recognized, Related Allowance	35	1
Cash Basis Interest Recognized, Related Allowance	35	1
Average Recorded Investment, No Related Allowance	1,636	2,130
Interest Income Recognized, No Related Allowance	10	0
Cash Basis Interest Recognized, No Related Allowance	10	0
Commercial Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	10,241	5,319
Interest Income Recognized, Related Allowance	0	0
Cash Basis Interest Recognized, Related Allowance	0	0
Average Recorded Investment, No Related Allowance	4,886	6,970
Interest Income Recognized, No Related Allowance	0	0
Cash Basis Interest Recognized, No Related Allowance	0	0
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Related Allowance	400	0
Interest Income Recognized, Related Allowance	2	8
Cash Basis Interest Recognized, Related Allowance	2	8
Average Recorded Investment, No Related Allowance	257	0
Interest Income Recognized, No Related Allowance	2	0
Cash Basis Interest Recognized, No Related Allowance	$ 2	$ 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 interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

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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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- Definition

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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