Loans - Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	$ 17,373	$ 16,234
Charge-offs	(762)	(650)
Recoveries	128	71
Provision (benefit) for loan losses	943us-gaap_ProvisionForLoanAndLeaseLosses	1,019us-gaap_ProvisionForLoanAndLeaseLosses
Allowances for loan losses, Ending Balance	17,682	16,674
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	7,114	8,212
Charge-offs	(74)	0
Recoveries	15	0
Provision (benefit) for loan losses	168	66
Allowances for loan losses, Ending Balance	7,223	8,278
Commercial Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	5,310	3,536
Charge-offs	0	(50)
Recoveries	50	0
Provision (benefit) for loan losses	(64)	218
Allowances for loan losses, Ending Balance	5,296	3,704
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	2,479	2,450
Charge-offs	(66)	(122)
Recoveries	1	19
Provision (benefit) for loan losses	372	108
Allowances for loan losses, Ending Balance	2,786	2,455
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	2,205	1,763
Charge-offs	(523)	(399)
Recoveries	29	22
Provision (benefit) for loan losses	418	586
Allowances for loan losses, Ending Balance	2,129	1,972
Credit Cards [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	71	66
Charge-offs	(42)	(21)
Recoveries	3	2
Provision (benefit) for loan losses	42	21
Allowances for loan losses, Ending Balance	74	68
Overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	194	207
Charge-offs	(57)	(58)
Recoveries	30	28
Provision (benefit) for loan losses	7	20
Allowances for loan losses, Ending Balance	$ 174	$ 197

A valuation allowance for financing receivables that are expected to be uncollectible.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(4)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

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-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

-Article 9

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

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-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 4: http://www.xbrl.org/2003/role/presentationRef

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