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Allowance for Loan losses - Impaired Loans and Related Allowance (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Financing Receivable, Impaired [Line Items] |  |
Unpaid Principal Balance | $ 8,456 | $ 15,376
Recorded Investment with No Allowance | 6,784 | 9,039
Recorded Investment with Allowance | 921 | 4,883
Total Recorded Investment | 7,705 | 13,922
Related Allowance | 544 | 1,907
Average Recorded Investment | 10,544 | 19,239
Interest Income Recognized | 225 | 385
Construction and Land Development [Member] |  |
Financing Receivable, Impaired [Line Items] |  |
Unpaid Principal Balance | 2,741 | 3,299
Recorded Investment with No Allowance | 2,206 | 2,800
Recorded Investment with Allowance | 338 | 405
Total Recorded Investment | 2,544 | 3,205
Related Allowance | 326 | 245
Average Recorded Investment | 2,967 | 5,532
Interest Income Recognized | 60 | 40
Secured by 1-4 Family Residential [Member] |  |
Financing Receivable, Impaired [Line Items] |  |
Unpaid Principal Balance | 2,116 | 4,327
Recorded Investment with No Allowance | 2,021 | 2,526
Recorded Investment with Allowance | 23 | 888
Total Recorded Investment | 2,044 | 3,414
Related Allowance | 23 | 173
Average Recorded Investment | 2,526 | 3,433
Interest Income Recognized | 107 | 138
Other Real Estate Loans [Member] |  |
Financing Receivable, Impaired [Line Items] |  |
Unpaid Principal Balance | 3,492 | 7,623
Recorded Investment with No Allowance | 2,463 | 3,708
Recorded Investment with Allowance | 560 | 3,475
Total Recorded Investment | 3,023 | 7,183
Related Allowance | 195 | 1,456
Average Recorded Investment | 4,933 | 10,115
Interest Income Recognized | 58 | 206
Commercial and Industrial [Member] |  |
Financing Receivable, Impaired [Line Items] |  |
Unpaid Principal Balance | 107 | 127
Recorded Investment with No Allowance | 94 | 5
Recorded Investment with Allowance |  | 115
Total Recorded Investment | 94 | 120
Related Allowance |  | 33
Average Recorded Investment | $ 118 | 159
Interest Income Recognized |  | $ 1

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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 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=49124121&loc=SL6953423-111524 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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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=49124121&loc=SL6953423-111524 + Details
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- Definition 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=49124121&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=49124121&loc=d3e5258-111524 + Details
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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 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)(2) -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524 + 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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524 + Details
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