Allowance for Loan Losses - Ending Allocation of Allowance for Loan Losses and Loan Balances Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with credit deterioration	$ 1,301
Individually evaluated for impairment	855	1,023
Individually evaluated for impairment	10,916	11,149
Collectively evaluated for impairment	13,460	13,245
Collectively evaluated for impairment	971,888	903,708
Ending balance	14,315	14,268	16,767	16,528
Ending balance	984,105	914,857
Commercial and Agriculture [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with credit deterioration	535
Individually evaluated for impairment	641	641
Individually evaluated for impairment	2,301	2,304
Collectively evaluated for impairment	1,153	1,181
Collectively evaluated for impairment	117,314	111,882
Ending balance	1,794	1,822	2,607	2,841
Ending balance	120,150	114,186
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with credit deterioration	83
Individually evaluated for impairment	4	57
Individually evaluated for impairment	4,351	3,557
Collectively evaluated for impairment	2,604	2,523
Collectively evaluated for impairment	161,073	139,457
Ending balance	2,608	2,580	3,829	3,263
Ending balance	165,507	143,014
Commercial Real Estate Non Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	4	20
Individually evaluated for impairment	2,070	2,175
Collectively evaluated for impairment	4,922	4,778
Collectively evaluated for impairment	316,963	306,491
Ending balance	4,926	4,798	4,168	4,296
Ending balance	319,033	308,666
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with credit deterioration	683
Individually evaluated for impairment	177	305
Individually evaluated for impairment	2,149	3,108
Collectively evaluated for impairment	3,489	3,442
Collectively evaluated for impairment	281,703	265,402
Ending balance	3,666	3,747	5,050	5,224
Ending balance	284,535	268,510
Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	29
Individually evaluated for impairment	40
Collectively evaluated for impairment	469	428
Collectively evaluated for impairment	75,042	65,452
Ending balance	498	428	295	184
Ending balance	75,082	65,452
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	5	5
Collectively evaluated for impairment	186	196
Collectively evaluated for impairment	19,793	15,024
Ending balance	186	196	239	214
Ending balance	19,798	15,029
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	637	697
Ending balance	$ 637	$ 697	$ 579	$ 506

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For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 4

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.4)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The valuation allowance for financing receivables acquired with deteriorated credit quality.

+ 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 (g)

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

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

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- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ 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 (h)

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

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- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ 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 (h)

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

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- Definition

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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

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