Allowance for Loan Losses - Ending Allocation of Allowance for Loan Losses and Loan Balances Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	$ 1,023	$ 2,509
Collectively evaluated for impairment	13,245	14,019
Ending Balance	14,268	16,528	19,742
Loan balances outstanding:
Individually evaluated for impairment	11,149	18,057
Collectively evaluated for impairment	903,708	843,184
Ending Balance	914,857	861,241
Commercial and Agriculture [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	641	1,262
Collectively evaluated for impairment	1,181	1,579
Ending Balance	1,822	2,841	2,811
Loan balances outstanding:
Individually evaluated for impairment	2,304	3,869
Collectively evaluated for impairment	111,882	112,006
Ending Balance	114,186	115,875
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	57	390
Collectively evaluated for impairment	2,523	2,873
Ending Balance	2,580	3,263	4,836
Loan balances outstanding:
Individually evaluated for impairment	3,557	6,792
Collectively evaluated for impairment	139,457	154,222
Ending Balance	143,014	161,014
Commercial Real Estate Non Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	20	55
Collectively evaluated for impairment	4,778	4,241
Ending Balance	4,798	4,296	5,303
Loan balances outstanding:
Individually evaluated for impairment	2,175	3,383
Collectively evaluated for impairment	306,491	279,449
Ending Balance	308,666	282,832
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	305	802
Collectively evaluated for impairment	3,442	4,422
Ending Balance	3,747	5,224	5,780
Loan balances outstanding:
Individually evaluated for impairment	3,108	4,005
Collectively evaluated for impairment	265,402	246,686
Ending Balance	268,510	250,691
Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	428	184
Ending Balance	428	184	349
Loan balances outstanding:
Collectively evaluated for impairment	65,452	39,964
Ending Balance	65,452	39,964
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	196	214
Ending Balance	196	214	246
Loan balances outstanding:
Individually evaluated for impairment	5	8
Collectively evaluated for impairment	15,024	10,857
Ending Balance	15,029	10,865
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	697	506
Ending Balance	$ 697	$ 506	$ 417

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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 that are expected to be uncollectible 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 (g)

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

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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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