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Allowance for Loan losses - Impaired Loans and Related Allowance (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 | Mar. 31, 2016 | Dec. 31, 2016
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | $ 5,219 | $ 8,686 | $ 5,545
Recorded Investment with No Allowance | 4,428 | 6,818 | 4,707
Recorded Investment with Allowance | 85 | 998 | 153
Total Recorded Investment | 4,513 | 7,816 | 4,860
Related Allowance | 31 | 434 | 37
Average Recorded Investment | 4,756 | 7,813 | 7,034
Interest Income Recognized | 49 | 48 | 176
Construction and Land Development [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | 2,455 | 2,897 | 2,388
Recorded Investment with No Allowance | 2,022 | 2,253 | 1,973
Recorded Investment with Allowance |  | 422 |
Total Recorded Investment | 2,022 | 2,675 | 1,973
Related Allowance |  | 222 |
Average Recorded Investment | 1,922 | 2,593 | 2,407
Interest Income Recognized | 13 | 16 | 66
Secured by 1-4 Family Residential [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | 1,469 | 2,136 | 1,851
Recorded Investment with No Allowance | 1,358 | 2,040 | 1,675
Recorded Investment with Allowance | 85 | 22 | 153
Total Recorded Investment | 1,443 | 2,062 | 1,828
Related Allowance | 31 | 22 | 37
Average Recorded Investment | 1,781 | 2,059 | 2,013
Interest Income Recognized | 16 | 24 | 87
Other Real Estate Loans [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | 1,206 | 3,549 | 1,213
Recorded Investment with No Allowance | 977 | 2,436 | 984
Recorded Investment with Allowance |  | 554 |
Total Recorded Investment | 977 | 2,990 | 984
Related Allowance |  | 190 |
Average Recorded Investment | 980 | 3,069 | 2,529
Interest Income Recognized | 19 | 8 | 22
Commercial and Industrial [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Unpaid Principal Balance | 89 | 104 | 93
Recorded Investment with No Allowance | 71 | 89 | 75
Total Recorded Investment | 71 | 89 | 75
Average Recorded Investment | 73 | $ 92 | 85
Interest Income Recognized | $ 1 |  | $ 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=66008989&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=66008989&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=66008989&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=66008989&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=66008989&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=66008989&loc=d3e5212-111524 + Details
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- Definition Amount of investment in impaired financing receivables for which there is no 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=66008989&loc=SL6953550-111524 + Details
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