<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.5.0.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>255</ContextCount>
  <ElementCount>256</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>47</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-document-and-entity-information</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>001 - Statement - Unaudited Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-unaudited-consolidated-balance-sheets</Role>
      <ShortName>Unaudited Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>002 - Statement - Unaudited Consolidated Balance Sheets (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-unaudited-consolidated-balance-sheets-parentheticals</Role>
      <ShortName>Unaudited Consolidated Balance Sheets (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>003 - Statement - Unaudited Consolidated Statements of Earnings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-unaudited-consolidated-statements-of-earnings</Role>
      <ShortName>Unaudited Consolidated Statements of Earnings</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>004 - Statement - Unaudited Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-unaudited-consolidated-statements-of-comprehensive-income</Role>
      <ShortName>Unaudited Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>005 - Statement - Unaudited Consolidated Statements of Comprehensive Income (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-unaudited-consolidated-statements-of-comprehensive-income-parentheticals</Role>
      <ShortName>Unaudited Consolidated Statements of Comprehensive Income (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>006 - Statement - Unaudited Consolidated Statements of Changes in Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-unaudited-consolidated-statements-of-changes-in-shareholders-equity</Role>
      <ShortName>Unaudited Consolidated Statements of Changes in Shareholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>007 - Statement - Unaudited Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-unaudited-consolidated-statements-of-cash-flows</Role>
      <ShortName>Unaudited Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>008 - Disclosure - Note 1 - Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-1-basis-of-presentation</Role>
      <ShortName>Note 1 - Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>009 - Disclosure - Note 2 - Reclassifications</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-2-reclassifications</Role>
      <ShortName>Note 2 - Reclassifications</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010 - Disclosure - Note 3 - Net Earnings Per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-3-net-earnings-per-common-share</Role>
      <ShortName>Note 3 - Net Earnings Per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>011 - Disclosure - Note 4 - Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-4-securities</Role>
      <ShortName>Note 4 - Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>012 - Disclosure - Note 5 - Loans, Allowance for Loan Losses and Credit Quality</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-5-loans-allowance-for-loan-losses-and-credit-quality</Role>
      <ShortName>Note 5 - Loans, Allowance for Loan Losses and Credit Quality</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>013 - Disclosure - Note 6 - Fair Value Measurements and Disclosures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-6-fair-value-measurements-and-disclosures</Role>
      <ShortName>Note 6 - Fair Value Measurements and Disclosures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>014 - Disclosure - Note 7 - Segment Reporting</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-7-segment-reporting</Role>
      <ShortName>Note 7 - Segment Reporting</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>015 - Disclosure - Note 8 - Goodwill and Intangibles</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-8-goodwill-and-intangibles</Role>
      <ShortName>Note 8 - Goodwill and Intangibles</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>016 - Disclosure - Note 9 - Cash and Cash Equivalents</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-9-cash-and-cash-equivalents</Role>
      <ShortName>Note 9 - Cash and Cash Equivalents</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>017 - Disclosure - Note 10 - Subordinated Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-10-subordinated-debt</Role>
      <ShortName>Note 10 - Subordinated Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>018 - Disclosure - Note 11 - Acquisition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-11-acquisition</Role>
      <ShortName>Note 11 - Acquisition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>019 - Disclosure - Note 12 - Change in Accounting Policy for Mortgage Loans Held-for-Sale</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-12-change-in-accounting-policy-for-mortgage-loans-heldforsale</Role>
      <ShortName>Note 12 - Change in Accounting Policy for Mortgage Loans Held-for-Sale</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>020 - Document - Note 13 - Recently Issued Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-13-recently-issued-accounting-pronouncements</Role>
      <ShortName>Note 13 - Recently Issued Accounting Pronouncements</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>021 - Disclosure - Note 3 - Net Earnings Per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-3-net-earnings-per-common-share-tables</Role>
      <ShortName>Note 3 - Net Earnings Per Common Share (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>022 - Disclosure - Note 4 - Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-4-securities-tables</Role>
      <ShortName>Note 4 - Securities (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>023 - Disclosure - Note 5 - Loans, Allowance for Loan Losses and Credit Quality (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-5-loans-allowance-for-loan-losses-and-credit-quality-tables</Role>
      <ShortName>Note 5 - Loans, Allowance for Loan Losses and Credit Quality (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>024 - Disclosure - Note 6 - Fair Value Measurements and Disclosures (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-6-fair-value-measurements-and-disclosures-tables</Role>
      <ShortName>Note 6 - Fair Value Measurements and Disclosures (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>025 - Disclosure - Note 7 - Segment Reporting (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-7-segment-reporting-tables</Role>
      <ShortName>Note 7 - Segment Reporting (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>026 - Disclosure - Note 8 - Goodwill and Intangibles (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-8-goodwill-and-intangibles-tables</Role>
      <ShortName>Note 8 - Goodwill and Intangibles (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>027 - Disclosure - Note 3 - Net Earnings Per Common Share (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-3-net-earnings-per-common-share-details-textual</Role>
      <ShortName>Note 3 - Net Earnings Per Common Share (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>028 - Disclosure - Note 3 - Net Earnings Per Common Share - Components of Basic and Diluted Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-3-net-earnings-per-common-share-components-of-basic-and-diluted-earnings-per-share-details</Role>
      <ShortName>Note 3 - Net Earnings Per Common Share - Components of Basic and Diluted Earnings Per Share (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>029 - Disclosure - Note 4 - Securities (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-4-securities-details-textual</Role>
      <ShortName>Note 4 - Securities (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>030 - Disclosure - Note 4 - Securities - Amorized Cost and Fair Value of Held-to-maturity Debt Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-4-securities-amorized-cost-and-fair-value-of-heldtomaturity-debt-securities-details</Role>
      <ShortName>Note 4 - Securities - Amorized Cost and Fair Value of Held-to-maturity Debt Securities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>031 - Disclosure - Note 4 - Securities - Amortized Cost and Fair Value of Available-for-sale Debt Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-4-securities-amortized-cost-and-fair-value-of-availableforsale-debt-securities-details</Role>
      <ShortName>Note 4 - Securities - Amortized Cost and Fair Value of Available-for-sale Debt Securities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>032 - Disclosure - Note 4 - Securities - Debt Securities with Unrealized Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-4-securities-debt-securities-with-unrealized-losses-details</Role>
      <ShortName>Note 4 - Securities - Debt Securities with Unrealized Losses (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>033 - Disclosure - Note 4 - Securities - Amortized Cost and Estimated Fair Value of Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-4-securities-amortized-cost-and-estimated-fair-value-of-securities-details</Role>
      <ShortName>Note 4 - Securities - Amortized Cost and Estimated Fair Value of Securities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>034 - Disclosure - Note 5 - Loans, Allowance for Loan Losses and Credit Quality (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-5-loans-allowance-for-loan-losses-and-credit-quality-details-textual</Role>
      <ShortName>Note 5 - Loans, Allowance for Loan Losses and Credit Quality (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>035 - Disclosure - Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Major Classification of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-5-loans-allowance-for-loan-losses-and-credit-quality-summary-of-major-classification-of-loans-details</Role>
      <ShortName>Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Major Classification of Loans (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>036 - Disclosure - Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Allowance for Loan Losses and Recorded Investment in Loans by Portfolio Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-5-loans-allowance-for-loan-losses-and-credit-quality-summary-of-allowance-for-loan-losses-and-recorded-investment-in-loans-by-portfolio-segment-details</Role>
      <ShortName>Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Allowance for Loan Losses and Recorded Investment in Loans by Portfolio Segment (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>037 - Disclosure - Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Impaired Loans by Class of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-5-loans-allowance-for-loan-losses-and-credit-quality-summary-of-impaired-loans-by-class-of-loans-details</Role>
      <ShortName>Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Impaired Loans by Class of Loans (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>038 - Disclosure - Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Aging of Recorded Investment in Past Due and Non-accrual Loan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-5-loans-allowance-for-loan-losses-and-credit-quality-summary-of-aging-of-recorded-investment-in-past-due-and-nonaccrual-loan-details</Role>
      <ShortName>Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Aging of Recorded Investment in Past Due and Non-accrual Loan (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>039 - Disclosure - Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Risk Category of Loans by Class of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-5-loans-allowance-for-loan-losses-and-credit-quality-summary-of-risk-category-of-loans-by-class-of-loans-details</Role>
      <ShortName>Note 5 - Loans, Allowance for Loan Losses and Credit Quality - Summary of Risk Category of Loans by Class of Loans (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>040 - Disclosure - Note 6 - Fair Value Measurements and Disclosures - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-6-fair-value-measurements-and-disclosures-assets-and-liabilities-measured-at-fair-value-on-a-recurring-basis-details</Role>
      <ShortName>Note 6 - Fair Value Measurements and Disclosures - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>041 - Disclosure - Note 6 - Fair Value Measurements and Disclosures - Assets Measured at Fair Value on a Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-6-fair-value-measurements-and-disclosures-assets-measured-at-fair-value-on-a-nonrecurring-basis-details</Role>
      <ShortName>Note 6 - Fair Value Measurements and Disclosures - Assets Measured at Fair Value on a Nonrecurring Basis (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>042 - Disclosure - Note 6 - Fair Value Measurements and Disclosures - Carrying Amounts and Estimated Fair Values of the Company's Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-6-fair-value-measurements-and-disclosures-carrying-amounts-and-estimated-fair-values-of-the-companys-financial-instruments-details</Role>
      <ShortName>Note 6 - Fair Value Measurements and Disclosures - Carrying Amounts and Estimated Fair Values of the Company's Financial Instruments (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>043 - Disclosure - Note 7 - Segment Reporting (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-7-segment-reporting-details-textual</Role>
      <ShortName>Note 7 - Segment Reporting (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>044 - Disclosure - Note 7 - Segment Reporting - Reconciliation of Reportable Segment Revenue, Expenses and Profit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-7-segment-reporting-reconciliation-of-reportable-segment-revenue-expenses-and-profit-details</Role>
      <ShortName>Note 7 - Segment Reporting - Reconciliation of Reportable Segment Revenue, Expenses and Profit (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>045 - Disclosure - Note 8 - Goodwill and Intangibles (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-8-goodwill-and-intangibles-details-textual</Role>
      <ShortName>Note 8 - Goodwill and Intangibles (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>046 - Disclosure - Note 8 Goodwill and Intangibles - Changes in Carrying Amount of Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-8-goodwill-and-intangibles-changes-in-carrying-amount-of-goodwill-details</Role>
      <ShortName>Note 8 Goodwill and Intangibles - Changes in Carrying Amount of Goodwill (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>047 - Disclosure - Note 8 - Goodwill and Intangibles - Core Deposit Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-8-goodwill-and-intangibles-core-deposit-intangible-assets-details</Role>
      <ShortName>Note 8 - Goodwill and Intangibles - Core Deposit Intangible Assets (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>048 - Disclosure - Note 9 - Cash and Cash Equivalents (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-9-cash-and-cash-equivalents-details-textual</Role>
      <ShortName>Note 9 - Cash and Cash Equivalents (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>049 - Disclosure - Note 10 - Subordinated Debt (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-10-subordinated-debt-details-textual</Role>
      <ShortName>Note 10 - Subordinated Debt (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>050 - Disclosure - Note 11 - Acquisition (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-11-acquisition-details-textual</Role>
      <ShortName>Note 11 - Acquisition (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="ncom-20160930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>051 - Disclosure - Note 12 - Change in Accounting Policy for Mortgage Loans Held-for-Sale (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nationalbankofcommerce.com/20160930/role/statement-note-12-change-in-accounting-policy-for-mortgage-loans-heldforsale-details-textual</Role>
      <ShortName>Note 12 - Change in Accounting Policy for Mortgage Loans Held-for-Sale (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>ncom-20160930.xml</File>
    <File>ncom-20160930.xsd</File>
    <File>ncom-20160930_cal.xml</File>
    <File>ncom-20160930_def.xml</File>
    <File>ncom-20160930_lab.xml</File>
    <File>ncom-20160930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
