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Allowance for Loan Losses - Impaired Loans and Related Allowance (Detail) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | $ 3,123 | $ 5,831 | $ 4,575
Recorded Investment with No Allowance | 2,513 | 4,995 | 3,811
Recorded Investment with Allowance | 494 | 0 | 0
Total Recorded Investment | 3,007 | 4,995 | 3,811
Related Allowance | 107 | 0 | 0
Average Recorded Investment | 3,634 | 4,755 | 4,656
Interest Income Recognized | 54 | 159 | 232
Real estate loans | Construction and Land Development |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | 343 | 2,429 | 1,627
Recorded Investment with No Allowance | 0 | 1,959 | 1,150
Recorded Investment with Allowance | 343 | 0 | 0
Total Recorded Investment | 343 | 1,959 | 1,150
Related Allowance | 87 | 0 | 0
Average Recorded Investment | 900 | 1,904 | 1,814
Interest Income Recognized | 12 | 40 | 63
Real estate loans | Secured by 1-4 Family Residential |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | 511 | 1,808 | 1,387
Recorded Investment with No Allowance | 287 | 1,654 | 1,307
Recorded Investment with Allowance | 151 | 0 | 0
Total Recorded Investment | 438 | 1,654 | 1,307
Related Allowance | 20 | 0 | 0
Average Recorded Investment | 1,172 | 1,697 | 1,637
Interest Income Recognized | 5 | 47 | 64
Real estate loans | Other real estate loans |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | 2,069 | 1,512 | 1,483
Recorded Investment with No Allowance | 2,029 | 1,319 | 1,289
Recorded Investment with Allowance | 0 | 0 | 0
Total Recorded Investment | 2,029 | 1,319 | 1,289
Related Allowance | 0 | 0 | 0
Average Recorded Investment | 1,433 | 1,084 | 1,137
Interest Income Recognized | 37 | 68 | 95
Commercial and industrial loans |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | 200 | 82 | 78
Recorded Investment with No Allowance | 197 | 63 | 65
Recorded Investment with Allowance | 0 | 0 | 0
Total Recorded Investment | 197 | 63 | 65
Related Allowance | 0 | 0 | 0
Average Recorded Investment | 129 | 70 | 68
Interest Income Recognized | $ 0 | $ 4 | $ 10

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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=84173941&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=84173941&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=84173941&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=84173941&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=84173941&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=84173941&loc=d3e5212-111524 + Details
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