Allowance for Loan Losses - Aging Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 3,288	$ 3,876
60-89 Days Past Due	985	1,305
90 Days or Greater	5,321	8,072
Total Past Due	9,594	13,253
Current	905,263	847,988
Ending Balance	914,857	861,241
Past Due 90 Days and Accruing	0	0
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	58	105
90 Days or Greater	187	443
Total Past Due	245	548
Current	113,941	115,327
Ending Balance	114,186	115,875
Past Due 90 Days and Accruing	0	0
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	622	253
60-89 Days Past Due	251	188
90 Days or Greater	657	1,643
Total Past Due	1,530	2,084
Current	141,484	158,930
Ending Balance	143,014	161,014
Past Due 90 Days and Accruing	0	0
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	521	208
60-89 Days Past Due	5	13
90 Days or Greater	2,103	455
Total Past Due	2,629	676
Current	306,037	282,156
Ending Balance	308,666	282,832
Past Due 90 Days and Accruing	0	0
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,923	3,140
60-89 Days Past Due	721	1,084
90 Days or Greater	2,347	5,531
Total Past Due	4,991	9,755
Current	263,519	240,936
Ending Balance	268,510	250,691
Past Due 90 Days and Accruing	0	0
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	33
90 Days or Greater	8
Total Past Due	41
Current	65,411	39,964
Ending Balance	65,452	39,964
Past Due 90 Days and Accruing	0	0
Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	131	170
60-89 Days Past Due	8	20
90 Days or Greater	19
Total Past Due	158	190
Current	14,871	10,675
Ending Balance	15,029	10,865
Past Due 90 Days and Accruing	$ 0	$ 0

Financing receivables that are less than 60 days past due but more than 29 days past due.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

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-Section 50

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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

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