Allowance for Loan losses - Impaired Loans and Related Allowance (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$ 26,072	$ 22,675	$ 32,317
Recorded Investment with No Allowance	16,343	7,198	15,161
Recorded Investment with Allowance	5,351	9,782	10,758
Total Recorded Investment	21,694	16,980	25,920
Related Allowance	1,379	1,838	2,438
Average Recorded Investment	16,009	20,990	38,174
Interest Income Recognized	805	548	1,091
Construction and Land Development [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	9,086	2,947	8,106
Recorded Investment with No Allowance	4,259	622	3,531
Recorded Investment with Allowance	2,603	1,894	4,109
Total Recorded Investment	6,862	2,516	7,640
Related Allowance	882	567	930
Average Recorded Investment	5,397	5,691	7,077
Interest Income Recognized	204	99	367
Secured by 1-4 Family Residential [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	4,341	4,706	8,566
Recorded Investment with No Allowance	2,515	1,690	3,495
Recorded Investment with Allowance	916	2,086	3,365
Total Recorded Investment	3,431	3,776	6,860
Related Allowance	190	306	848
Average Recorded Investment	2,864	4,821	6,519
Interest Income Recognized	146	163	301
Other Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	12,385	14,861	15,165
Recorded Investment with No Allowance	9,455	4,886	8,135
Recorded Investment with Allowance	1,688	5,642	2,805
Total Recorded Investment	11,143	10,528	10,940
Related Allowance	263	930	351
Average Recorded Investment	7,079	10,148	23,918
Interest Income Recognized	441	276	396
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	260	161	480
Recorded Investment with No Allowance	114
Recorded Investment with Allowance	144	160	480
Total Recorded Investment	258	160	480
Related Allowance	44	35	309
Average Recorded Investment	669	330	660
Interest Income Recognized	14	10	27
Consumer and Other Loans [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance
Recorded Investment with No Allowance
Recorded Investment with Allowance
Total Recorded Investment
Related Allowance
Average Recorded Investment
Interest Income Recognized

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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=28368275&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=28368275&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

+ Details

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- Definition

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 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953550-111524

+ Details

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

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- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

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