<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.8.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>685</ContextCount>
  <ElementCount>488</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>221</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>10</UnitCount>
  <MyReports>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document and Entity Information Document</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DocumentAndEntityInformationDocument</Role>
      <ShortName>Document and Entity Information Document</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001501 - Statement - Consolidated Balance Sheets (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ConsolidatedBalanceSheetsParentheticals</Role>
      <ShortName>Consolidated Balance Sheets (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002000 - Statement - Consolidated Statements of Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ConsolidatedStatementsOfIncome</Role>
      <ShortName>Consolidated Statements of Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004000 - Statement - Consolidated Statements of Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ConsolidatedStatementsOfShareholdersEquity</Role>
      <ShortName>Consolidated Statements of Shareholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1004501 - Statement - Consolidated Statements of Shareholders' Equity (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ConsolidatedStatementsOfShareholdersEquityParentheticals</Role>
      <ShortName>Consolidated Statements of Shareholders' Equity (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1005000 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Description of Business</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DescriptionOfBusiness</Role>
      <ShortName>Description of Business</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Recent Developments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/RecentDevelopments</Role>
      <ShortName>Recent Developments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Summary of Significant Accounting Policies and Practices</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPractices</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - Loans Receivable and Allowance for Loan Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/LoansReceivableAndAllowanceForLoanLosses</Role>
      <ShortName>Loans Receivable and Allowance for Loan Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2106100 - Disclosure - Bonds and Notes Payable</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayable</Role>
      <ShortName>Bonds and Notes Payable</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - Derivative Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstruments</Role>
      <ShortName>Derivative Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2110100 - Disclosure - Investments and Notes Receivable</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/InvestmentsAndNotesReceivable</Role>
      <ShortName>Investments and Notes Receivable</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2111100 - Disclosure - Business Combination</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/BusinessCombination</Role>
      <ShortName>Business Combination</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IntangibleAssets</Role>
      <ShortName>Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - Goodwill</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/Goodwill</Role>
      <ShortName>Goodwill</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2114100 - Disclosure - Property and Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/PropertyAndEquipment</Role>
      <ShortName>Property and Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2115100 - Disclosure - Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ShareholdersEquity</Role>
      <ShortName>Shareholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2116100 - Disclosure - Earnings per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/EarningsPerCommonShare</Role>
      <ShortName>Earnings per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2117100 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2118100 - Disclosure - Segment Reporting</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SegmentReporting</Role>
      <ShortName>Segment Reporting</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2120100 - Disclosure - Major Customer</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/MajorCustomer</Role>
      <ShortName>Major Customer</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2121100 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2128100 - Disclosure - Defined Contribution Benefit Plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DefinedContributionBenefitPlan</Role>
      <ShortName>Defined Contribution Benefit Plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2129100 - Disclosure - Stock Based Compensation Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/StockBasedCompensationPlans</Role>
      <ShortName>Stock Based Compensation Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2130100 - Disclosure - Related Parties</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/RelatedParties</Role>
      <ShortName>Related Parties</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2131100 - Disclosure - Fair Value</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/FairValue</Role>
      <ShortName>Fair Value</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2132100 - Disclosure - Legal Proceedings Legal Proceedings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/LegalProceedingsLegalProceedings</Role>
      <ShortName>Legal Proceedings Legal Proceedings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2133100 - Disclosure - Quarterly Financial Information (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/QuarterlyFinancialInformationUnaudited</Role>
      <ShortName>Quarterly Financial Information (Unaudited)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2134100 - Disclosure - Condensed Parent Company Financial Statements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/CondensedParentCompanyFinancialStatements</Role>
      <ShortName>Condensed Parent Company Financial Statements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2203201 - Disclosure - Summary of Significant Accounting Policies and Practices Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPracticesSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPractices</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2304301 - Disclosure - Loans Receivable and Allowance for Loan Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/LoansReceivableAndAllowanceForLoanLossesTables</Role>
      <ShortName>Loans Receivable and Allowance for Loan Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/LoansReceivableAndAllowanceForLoanLosses</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2306301 - Disclosure - Bonds and Notes payable (Tables)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayableTables</Role>
      <ShortName>Bonds and Notes payable (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - Derivative Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsTables</Role>
      <ShortName>Derivative Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/DerivativeFinancialInstruments</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2310301 - Disclosure - Investments and Notes Receivables (Tables)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/InvestmentsAndNotesReceivablesTables</Role>
      <ShortName>Investments and Notes Receivables (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/InvestmentsAndNotesReceivable</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2311301 - Disclosure - Business Combination (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/BusinessCombinationTables</Role>
      <ShortName>Business Combination (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/BusinessCombination</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2312301 - Disclosure - Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IntangibleAssetsTables</Role>
      <ShortName>Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/IntangibleAssets</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2313301 - Disclosure - Goodwill (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/GoodwillTables</Role>
      <ShortName>Goodwill (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/Goodwill</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2314301 - Disclosure - Property and Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/PropertyAndEquipmentTables</Role>
      <ShortName>Property and Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/PropertyAndEquipment</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2315301 - Disclosure - Shareholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ShareholdersEquityTables</Role>
      <ShortName>Shareholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/ShareholdersEquity</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2316301 - Disclosure - Earnings per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/EarningsPerCommonShareTables</Role>
      <ShortName>Earnings per Common Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/EarningsPerCommonShare</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2317301 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/IncomeTaxes</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2318301 - Disclosure - Segment Reporting (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SegmentReportingTables</Role>
      <ShortName>Segment Reporting (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/SegmentReporting</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2321301 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/Leases</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2329301 - Disclosure - Stock Based Compensation Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/StockBasedCompensationPlansTables</Role>
      <ShortName>Stock Based Compensation Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/StockBasedCompensationPlans</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2331301 - Disclosure - Fair Value (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/FairValueTables</Role>
      <ShortName>Fair Value (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/FairValue</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2333301 - Disclosure - Quarterly Financial Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/QuarterlyFinancialInformationTables</Role>
      <ShortName>Quarterly Financial Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/QuarterlyFinancialInformationUnaudited</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2334301 - Disclosure - Condensed Parent Company Financial Statements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/CondensedParentCompanyFinancialStatementsTables</Role>
      <ShortName>Condensed Parent Company Financial Statements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/CondensedParentCompanyFinancialStatements</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2401401 - Disclosure - Description of Business - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DescriptionOfBusinessNarrativeDetails</Role>
      <ShortName>Description of Business - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2402401 - Disclosure - Recent Developments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/RecentDevelopmentsDetails</Role>
      <ShortName>Recent Developments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/RecentDevelopments</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2403402 - Disclosure - Summary of Significant Accounting Policies and Practices - Variable Interest Entities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPracticesVariableInterestEntitiesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices - Variable Interest Entities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2403403 - Disclosure - Summary of Significant Accounting Policies and Practices - Noncontrolling Interest (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPracticesNoncontrollingInterestDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices - Noncontrolling Interest (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2403404 - Disclosure - Summary of Significant Accounting Policies and Practices - Loans Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPracticesLoansReceivableDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices - Loans Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2403405 - Disclosure - Summary of Significant Accounting Policies and Practices - Allowance for Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPracticesAllowanceForLoanLossesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices - Allowance for Loan Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2403406 - Disclosure - Summary of Significant Accounting Policies and Practices - Cash and Cash Equivalents and Statement of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPracticesCashAndCashEquivalentsAndStatementOfCashFlowsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices - Cash and Cash Equivalents and Statement of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2403407 - Disclosure - Summary of Significant Accounting Policies and Practices - Revenue Recognition (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPracticesRevenueRecognitionDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices - Revenue Recognition (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2403408 - Disclosure - Summary of Significant Accounting Policies and Practices - Compensation Expense for Stock Bases Awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SummaryOfSignificantAccountingPoliciesAndPracticesCompensationExpenseForStockBasesAwardsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Practices - Compensation Expense for Stock Bases Awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2404402 - Disclosure - Loans Receivable and Allowance for Loan Losses - Loans Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/LoansReceivableAndAllowanceForLoanLossesLoansReceivableDetails</Role>
      <ShortName>Loans Receivable and Allowance for Loan Losses - Loans Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2404403 - Disclosure - Loans Receivable and Allowance for Loan Losses - Activity in the Allowance for Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/LoansReceivableAndAllowanceForLoanLossesActivityInAllowanceForLoanLossesDetails</Role>
      <ShortName>Loans Receivable and Allowance for Loan Losses - Activity in the Allowance for Loan Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2404404 - Disclosure - Loans Receivable and Allowance for Loan Losses - Student Loan Status and Delinquency (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/LoansReceivableAndAllowanceForLoanLossesStudentLoanStatusAndDelinquencyDetails</Role>
      <ShortName>Loans Receivable and Allowance for Loan Losses - Student Loan Status and Delinquency (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2406402 - Disclosure - Bonds and Notes Payable - Outstanding Debt Obligations (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayableOutstandingDebtObligationsDetails</Role>
      <ShortName>Bonds and Notes Payable - Outstanding Debt Obligations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2406403 - Disclosure - Bonds and Notes Payable - Bonds and Notes Payable Outstanding Lines of Credit (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayableBondsAndNotesPayableOutstandingLinesOfCreditDetails</Role>
      <ShortName>Bonds and Notes Payable - Bonds and Notes Payable Outstanding Lines of Credit (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2406404 - Disclosure - Bonds and Notes Payable - Bonds and Notes Payable Asset-backed Securitizations (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayableBondsAndNotesPayableAssetBackedSecuritizationsDetails</Role>
      <ShortName>Bonds and Notes Payable - Bonds and Notes Payable Asset-backed Securitizations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2406405 - Disclosure - Bonds and Notes Payable - Narrative (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayableNarrativeDetails</Role>
      <ShortName>Bonds and Notes Payable - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2406406 - Disclosure - Bonds and Notes Payable - Schedule of TDP Notes Outstanding (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayableScheduleOfTdpNotesOutstandingDetails</Role>
      <ShortName>Bonds and Notes Payable - Schedule of TDP Notes Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2406407 - Disclosure - Bonds and Notes Payable - Maturity of long-term debt (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayableMaturityOfLongTermDebtDetails</Role>
      <ShortName>Bonds and Notes Payable - Maturity of long-term debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2406408 - Disclosure - Bonds and Notes Payable - Debt Repurchases (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/BondsAndNotesPayableDebtRepurchasesDetails</Role>
      <ShortName>Bonds and Notes Payable - Debt Repurchases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - Derivative Financial Instruments - Basis Swap (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsBasisSwapDetails</Role>
      <ShortName>Derivative Financial Instruments - Basis Swap (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Derivative Financial Instruments - Interest Rate Swaps, Floor Income Hedge (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsInterestRateSwapsFloorIncomeHedgeDetails</Role>
      <ShortName>Derivative Financial Instruments - Interest Rate Swaps, Floor Income Hedge (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>2407404 - Disclosure - Derivative Financial Instruments - Interest Rate Caps (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsInterestRateCapsDetails</Role>
      <ShortName>Derivative Financial Instruments - Interest Rate Caps (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>2407405 - Disclosure - Derivative Financial Instruments - Interest Rate Swaps, Unsecured Debt Hedges (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsInterestRateSwapsUnsecuredDebtHedgesDetails</Role>
      <ShortName>Derivative Financial Instruments - Interest Rate Swaps, Unsecured Debt Hedges (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>2407406 - Disclosure - Derivative Financial Instruments - Cross-currency Interest Rate Swaps (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsCrossCurrencyInterestRateSwapsDetails</Role>
      <ShortName>Derivative Financial Instruments - Cross-currency Interest Rate Swaps (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>2407407 - Disclosure - Derivative Financial Instruments - Fair Value of Derivative Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsFairValueOfDerivativeInstrumentsDetails</Role>
      <ShortName>Derivative Financial Instruments - Fair Value of Derivative Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>2407408 - Disclosure - Derivative Financial Instruments - Gross/Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsGrossNetDetails</Role>
      <ShortName>Derivative Financial Instruments - Gross/Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>2407409 - Disclosure - Derivative Financial Instruments - Income Statement Effect of Derivative Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DerivativeFinancialInstrumentsIncomeStatementEffectOfDerivativeInstrumentsDetails</Role>
      <ShortName>Derivative Financial Instruments - Income Statement Effect of Derivative Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>2410402 - Disclosure - Investments and Notes Receivable - Investments and Other Receivables Summary (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/InvestmentsAndNotesReceivableInvestmentsAndOtherReceivablesSummaryDetails</Role>
      <ShortName>Investments and Notes Receivable - Investments and Other Receivables Summary (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>2410403 - Disclosure - Investments and Notes Receivable - Realized and Unrealized Gains (Losses) on Investments (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nelnet.com/role/InvestmentsAndNotesReceivableRealizedAndUnrealizedGainsLossesOnInvestmentsDetails</Role>
      <ShortName>Investments and Notes Receivable - Realized and Unrealized Gains (Losses) on Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>2411402 - Disclosure - Business Combination - Acquisition Details (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/BusinessCombinationAcquisitionDetailsDetails</Role>
      <ShortName>Business Combination - Acquisition Details (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>2411403 - Disclosure - Business Combination - Schedule of Assets Acquired at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/BusinessCombinationScheduleOfAssetsAcquiredAtFairValueDetails</Role>
      <ShortName>Business Combination - Schedule of Assets Acquired at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>2412402 - Disclosure - Intangible Assets - Schedule of Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IntangibleAssetsScheduleOfIntangibleAssetsDetails</Role>
      <ShortName>Intangible Assets - Schedule of Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>2412403 - Disclosure - Intangible Assets - Schedule of Intangible Assets Future Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IntangibleAssetsScheduleOfIntangibleAssetsFutureAmortizationExpenseDetails</Role>
      <ShortName>Intangible Assets - Schedule of Intangible Assets Future Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>2413402 - Disclosure - Goodwill - Schedule of Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/GoodwillScheduleOfGoodwillDetails</Role>
      <ShortName>Goodwill - Schedule of Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>2413403 - Disclosure - Goodwill - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/GoodwillNarrativeDetails</Role>
      <ShortName>Goodwill - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>2414402 - Disclosure - Property and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/PropertyAndEquipmentDetails</Role>
      <ShortName>Property and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/PropertyAndEquipmentTables</ParentRole>
      <Position>86</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>2415402 - Disclosure - Shareholders' Equity - Classes of Common Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ShareholdersEquityClassesOfCommonStockDetails</Role>
      <ShortName>Shareholders' Equity - Classes of Common Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>2415403 - Disclosure - Shareholders' Equity - Schedule of Stock Repurchases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/ShareholdersEquityScheduleOfStockRepurchasesDetails</Role>
      <ShortName>Shareholders' Equity - Schedule of Stock Repurchases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>2416402 - Disclosure - Earnings per Common Share - Schedule of Earnings per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/EarningsPerCommonShareScheduleOfEarningsPerCommonShareDetails</Role>
      <ShortName>Earnings per Common Share - Schedule of Earnings per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>2417402 - Disclosure - Income Taxes - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IncomeTaxesNarrativeDetails</Role>
      <ShortName>Income Taxes - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>2417403 - Disclosure - Income Taxes - Schedule of Unrecognized Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IncomeTaxesScheduleOfUnrecognizedTaxBenefitsDetails</Role>
      <ShortName>Income Taxes - Schedule of Unrecognized Tax Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>2417404 - Disclosure - Income Taxes - Schedule of Provision for Income Tax Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IncomeTaxesScheduleOfProvisionForIncomeTaxExpenseDetails</Role>
      <ShortName>Income Taxes - Schedule of Provision for Income Tax Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>2417405 - Disclosure - Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IncomeTaxesScheduleOfEffectiveIncomeTaxRateReconciliationDetails</Role>
      <ShortName>Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>2417406 - Disclosure - Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/IncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesDetails</Role>
      <ShortName>Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>2418402 - Disclosure - Segment Reporting (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/SegmentReportingDetails</Role>
      <ShortName>Segment Reporting (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/SegmentReportingTables</ParentRole>
      <Position>95</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>2420401 - Disclosure - Major Customer (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/MajorCustomerDetails</Role>
      <ShortName>Major Customer (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/MajorCustomer</ParentRole>
      <Position>96</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>2421402 - Disclosure - Leases - Schedule of future Minimum Lease Payments for Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/LeasesScheduleOfFutureMinimumLeasePaymentsForOperatingLeasesDetails</Role>
      <ShortName>Leases - Schedule of future Minimum Lease Payments for Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>2428401 - Disclosure - Defined Contribution Benefit Plan Defined Contribution Benefit Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/DefinedContributionBenefitPlanDefinedContributionBenefitPlanDetails</Role>
      <ShortName>Defined Contribution Benefit Plan Defined Contribution Benefit Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>2429402 - Disclosure - Stock Based Compensation Plans - Restricted Stock and Employee Share Purchase Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/StockBasedCompensationPlansRestrictedStockAndEmployeeSharePurchasePlanDetails</Role>
      <ShortName>Stock Based Compensation Plans - Restricted Stock and Employee Share Purchase Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>2429403 - Disclosure - Stock Based Compensation Plans - Non-employee Directors Compensation Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/StockBasedCompensationPlansNonEmployeeDirectorsCompensationPlanDetails</Role>
      <ShortName>Stock Based Compensation Plans - Non-employee Directors Compensation Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>2430401 - Disclosure - Related Parties - Transactions with Union Bank and Trust Company (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/RelatedPartiesTransactionsWithUnionBankAndTrustCompanyDetails</Role>
      <ShortName>Related Parties - Transactions with Union Bank and Trust Company (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>2430402 - Disclosure - Related Parties - Related Party Transactions Investment Services (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/RelatedPartiesRelatedPartyTransactionsInvestmentServicesDetails</Role>
      <ShortName>Related Parties - Related Party Transactions Investment Services (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>102</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>2430403 - Disclosure - Related Parties - Transactions with Agile Sports Technologies, Inc. (doing business as "Hudl") (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/RelatedPartiesTransactionsWithAgileSportsTechnologiesIncDoingBusinessAsHudlDetails</Role>
      <ShortName>Related Parties - Transactions with Agile Sports Technologies, Inc. (doing business as "Hudl") (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>2431402 - Disclosure - Fair Value - Assets and Liabilities that are Measured at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/FairValueAssetsAndLiabilitiesThatAreMeasuredAtFairValueDetails</Role>
      <ShortName>Fair Value - Assets and Liabilities that are Measured at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>104</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>2431403 - Disclosure - Fair Value - Fair Value of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/FairValueFairValueOfFinancialInstrumentsDetails</Role>
      <ShortName>Fair Value - Fair Value of Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>105</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>2433402 - Disclosure - Quarterly Financial Information (Unaudited) Quarterly Financial Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/QuarterlyFinancialInformationUnauditedQuarterlyFinancialInformationDetails</Role>
      <ShortName>Quarterly Financial Information (Unaudited) Quarterly Financial Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.nelnet.com/role/QuarterlyFinancialInformationTables</ParentRole>
      <Position>106</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R107.htm</HtmlFileName>
      <LongName>2434402 - Disclosure - Condensed Parent Company Financial Statements - Condensed Parent Balance Sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/CondensedParentCompanyFinancialStatementsCondensedParentBalanceSheetsDetails</Role>
      <ShortName>Condensed Parent Company Financial Statements - Condensed Parent Balance Sheets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>107</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R108.htm</HtmlFileName>
      <LongName>2434403 - Disclosure - Condensed Parent Company Financial Statements - Condensed Parent Statements of Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/CondensedParentCompanyFinancialStatementsCondensedParentStatementsOfIncomeDetails</Role>
      <ShortName>Condensed Parent Company Financial Statements - Condensed Parent Statements of Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>108</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>2434404 - Disclosure - Condensed Parent Company Financial Statements - Condensed Parent Statement of Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/CondensedParentCompanyFinancialStatementsCondensedParentStatementOfComprehensiveIncomeDetails</Role>
      <ShortName>Condensed Parent Company Financial Statements - Condensed Parent Statement of Comprehensive Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>109</Position>
    </Report>
    <Report instance="nni-20171231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>2434405 - Disclosure - Condensed Parent Company Financial Statements - Condensed Parent Statements of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nelnet.com/role/CondensedParentCompanyFinancialStatementsCondensedParentStatementsOfCashFlowsDetails</Role>
      <ShortName>Condensed Parent Company Financial Statements - Condensed Parent Statements of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>110</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>nni-20171231.xml</File>
    <File>nni-20171231.xsd</File>
    <File>nni-20171231_cal.xml</File>
    <File>nni-20171231_def.xml</File>
    <File>nni-20171231_lab.xml</File>
    <File>nni-20171231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2014-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2017-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/invest/2013-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
