<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.6.0.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>482</ContextCount>
  <ElementCount>573</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>93</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>9</UnitCount>
  <MyReports>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - Consolidated Balance Sheet</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/StatementConsolidatedBalanceSheet</Role>
      <ShortName>Consolidated Balance Sheet</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - Consolidated Balance Sheet (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/StatementConsolidatedBalanceSheetParenthetical</Role>
      <ShortName>Consolidated Balance Sheet (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - Consolidated Statements of Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/StatementConsolidatedStatementsOfIncome</Role>
      <ShortName>Consolidated Statements of Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - Consolidated Statements Of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/StatementConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>Consolidated Statements Of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - Consolidated Statement of Changes in Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/StatementConsolidatedStatementOfChangesInShareholdersEquity</Role>
      <ShortName>Consolidated Statement of Changes in Shareholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00405 - Statement - Consolidated Statement of Changes in Shareholders' Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/StatementConsolidatedStatementOfChangesInShareholdersEquityParenthetical</Role>
      <ShortName>Consolidated Statement of Changes in Shareholders' Equity (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>00500 - Statement - Consolidated Statement of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/StatementConsolidatedStatementOfCashFlows</Role>
      <ShortName>Consolidated Statement of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10101 - Disclosure - Organization And Summary Of Signficant Accounting And Reporting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignficantAccountingAndReportingPolicies</Role>
      <ShortName>Organization And Summary Of Signficant Accounting And Reporting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Earnings Per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEarningsPerCommonShare</Role>
      <ShortName>Earnings Per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Acquisitions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureAcquisitions</Role>
      <ShortName>Acquisitions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Cash and Cash Equivalents</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureCashAndCashEquivalents</Role>
      <ShortName>Cash and Cash Equivalents</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecurities</Role>
      <ShortName>Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Loans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoans</Role>
      <ShortName>Loans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Allowance For Loan Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureAllowanceForLoanLosses</Role>
      <ShortName>Allowance For Loan Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Premises and Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosurePremisesAndEquipment</Role>
      <ShortName>Premises and Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Goodwill and Core Deposit Intangibles</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureGoodwillAndCoreDepositIntangibles</Role>
      <ShortName>Goodwill and Core Deposit Intangibles</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDeposits</Role>
      <ShortName>Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Securities sold under agreements to repurchase and Other Borrowed Funds</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecuritiesSoldUnderAgreementsToRepurchaseAndOtherBorrowedFunds</Role>
      <ShortName>Securities sold under agreements to repurchase and Other Borrowed Funds</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Subordinated Debentures and Subordinated Notes</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSubordinatedDebenturesAndSubordinatedNotes</Role>
      <ShortName>Subordinated Debentures and Subordinated Notes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11301 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11401 - Disclosure - Employee Benefits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefits</Role>
      <ShortName>Employee Benefits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11501 - Disclosure - Off-Balance Sheet Arrangements, Commitments And Ccontingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndCcontingencies</Role>
      <ShortName>Off-Balance Sheet Arrangements, Commitments And Ccontingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11601 - Disclosure - Derivative Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDerivativeFinancialInstruments</Role>
      <ShortName>Derivative Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>11701 - Disclosure - Regulatory Matters</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureRegulatoryMatters</Role>
      <ShortName>Regulatory Matters</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>11801 - Disclosure - Disclosures About Fair Value of Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDisclosuresAboutFairValueOfFinancialInstruments</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>11901 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>12001 - Disclosure - Parent Company Only Financial Statements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureParentCompanyOnlyFinancialStatements</Role>
      <ShortName>Parent Company Only Financial Statements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>20102 - Disclosure - Organization and Summary of Significant Accounting and Reporting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingAndReportingPoliciesPolicies</Role>
      <ShortName>Organization and Summary of Significant Accounting and Reporting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignficantAccountingAndReportingPolicies</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>30203 - Disclosure - Earnings Per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEarningsPerCommonShareTables</Role>
      <ShortName>Earnings Per Common Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureEarningsPerCommonShare</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>30303 - Disclosure - Acquisitions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureAcquisitionsTables</Role>
      <ShortName>Acquisitions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureAcquisitions</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>30503 - Disclosure - Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecuritiesTables</Role>
      <ShortName>Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureSecurities</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>30603 - Disclosure - Loans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansTables</Role>
      <ShortName>Loans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureLoans</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>30703 - Disclosure - Allowance For Loan Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureAllowanceForLoanLossesTables</Role>
      <ShortName>Allowance For Loan Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureAllowanceForLoanLosses</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>30803 - Disclosure - Premises and Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosurePremisesAndEquipmentTables</Role>
      <ShortName>Premises and Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosurePremisesAndEquipment</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>30903 - Disclosure - Goodwill and Core Deposit Intangibles (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureGoodwillAndCoreDepositIntangiblesTables</Role>
      <ShortName>Goodwill and Core Deposit Intangibles (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureGoodwillAndCoreDepositIntangibles</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>31003 - Disclosure - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDepositsTables</Role>
      <ShortName>Deposits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureDeposits</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>31103 - Disclosure - Securities sold under agreements to repurchase and Other Borrowed Funds (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecuritiesSoldUnderAgreementsToRepurchaseAndOtherBorrowedFundsTables</Role>
      <ShortName>Securities sold under agreements to repurchase and Other Borrowed Funds (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureSecuritiesSoldUnderAgreementsToRepurchaseAndOtherBorrowedFunds</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>31203 - Disclosure - Subordinated Debentures and Subordinated Notes (Tables)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSubordinatedDebenturesAndSubordinatedNotesTables</Role>
      <ShortName>Subordinated Debentures and Subordinated Notes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureSubordinatedDebenturesAndSubordinatedNotes</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>31303 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureIncomeTaxes</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>31403 - Disclosure - Employee Benefits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefitsTables</Role>
      <ShortName>Employee Benefits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureEmployeeBenefits</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>31503 - Disclosure - Off-Balance Sheet Arrangements, Commitments And Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndContingenciesTables</Role>
      <ShortName>Off-Balance Sheet Arrangements, Commitments And Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndCcontingencies</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>31603 - Disclosure - Derivative Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDerivativeFinancialInstrumentsTables</Role>
      <ShortName>Derivative Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureDerivativeFinancialInstruments</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>31703 - Disclosure - Regulatory Matters (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureRegulatoryMattersTables</Role>
      <ShortName>Regulatory Matters (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureRegulatoryMatters</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>31803 - Disclosure - Disclosures About Fair Value of Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDisclosuresAboutFairValueOfFinancialInstrumentsTables</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureDisclosuresAboutFairValueOfFinancialInstruments</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>32003 - Disclosure - Parent Company Only Financial Statements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureParentCompanyOnlyFinancialStatementsTables</Role>
      <ShortName>Parent Company Only Financial Statements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureParentCompanyOnlyFinancialStatements</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>40101 - Disclosure - Organization and Summary of Significant Accounting and Reporting Policies - Segments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingAndReportingPoliciesSegmentsDetails</Role>
      <ShortName>Organization and Summary of Significant Accounting and Reporting Policies - Segments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingAndReportingPoliciesPolicies</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>40102 - Disclosure - Organization and Summary of Significant Accounting and Reporting Policies - Initial Public Offering (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingAndReportingPoliciesInitialPublicOfferingDetails</Role>
      <ShortName>Organization and Summary of Significant Accounting and Reporting Policies - Initial Public Offering (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>40103 - Disclosure - Organization and Summary of Significant Accounting and Reporting Policies - Premises and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingAndReportingPoliciesPremisesAndEquipmentDetails</Role>
      <ShortName>Organization and Summary of Significant Accounting and Reporting Policies - Premises and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>40104 - Disclosure - Organization and Summary of Significant Accounting and Reporting Policies - Goodwill and Other Intangibles (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingAndReportingPoliciesGoodwillAndOtherIntangiblesDetails</Role>
      <ShortName>Organization and Summary of Significant Accounting and Reporting Policies - Goodwill and Other Intangibles (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>40105 - Disclosure - Organization and Summary of Significant Accounting and Reporting Policies - Guaranteed Portion of Loans, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingAndReportingPoliciesGuaranteedPortionOfLoansNetDetails</Role>
      <ShortName>Organization and Summary of Significant Accounting and Reporting Policies - Guaranteed Portion of Loans, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>40201 - Disclosure - Earnings Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEarningsPerCommonShareDetails</Role>
      <ShortName>Earnings Per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureEarningsPerCommonShareTables</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>40301 - Disclosure - Acquisitions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureAcquisitionsDetails</Role>
      <ShortName>Acquisitions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureAcquisitionsTables</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>40401 - Disclosure - Cash and Cash Equivalents (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureCashAndCashEquivalentsDetails</Role>
      <ShortName>Cash and Cash Equivalents (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureCashAndCashEquivalents</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>40501 - Disclosure - Securities - Amortized Cost and Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecuritiesAmortizedCostAndFairValueDetails</Role>
      <ShortName>Securities - Amortized Cost and Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>40502 - Disclosure - Securities - Contractual Maturities of Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecuritiesContractualMaturitiesOfSecuritiesDetails</Role>
      <ShortName>Securities - Contractual Maturities of Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>40503 - Disclosure - Securities - Securities in Continuous Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecuritiesSecuritiesInContinuousUnrealizedLossPositionDetails</Role>
      <ShortName>Securities - Securities in Continuous Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>40504 - Disclosure - Securities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecuritiesAdditionalInformationDetails</Role>
      <ShortName>Securities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>40601 - Disclosure - Loans - Portfolio by Type and Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansPortfolioByTypeAndClassDetails</Role>
      <ShortName>Loans - Portfolio by Type and Class (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>40602 - Disclosure - Loans - Other (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansOtherDetails</Role>
      <ShortName>Loans - Other (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>40603 - Disclosure - Loans - Maturities and Rate Sensitivity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansMaturitiesAndRateSensitivityDetails</Role>
      <ShortName>Loans - Maturities and Rate Sensitivity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>40604 - Disclosure - Loans - Related Party Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansRelatedPartyLoansDetails</Role>
      <ShortName>Loans - Related Party Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>40605 - Disclosure - Loans - Acquired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansAcquiredLoansDetails</Role>
      <ShortName>Loans - Acquired Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>40606 - Disclosure - Loans - Age Analysis of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansAgeAnalysisOfLoansDetails</Role>
      <ShortName>Loans - Age Analysis of Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>40607 - Disclosure - Loans - Impaired Loans Summary (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansImpairedLoansSummaryDetails</Role>
      <ShortName>Loans - Impaired Loans Summary (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>40608 - Disclosure - Loans - Average recorded investment and interest income recognized (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansAverageRecordedInvestmentAndInterestIncomeRecognizedDetails</Role>
      <ShortName>Loans - Average recorded investment and interest income recognized (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>40609 - Disclosure - Loans - Impaired Loans Individually Evaluated (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansImpairedLoansIndividuallyEvaluatedDetails</Role>
      <ShortName>Loans - Impaired Loans Individually Evaluated (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>40610 - Disclosure - Loans - Credit Quality (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansCreditQualityDetails</Role>
      <ShortName>Loans - Credit Quality (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>40611 - Disclosure - Loans - Troubled Debt Restructurings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureLoansTroubledDebtRestructuringsDetails</Role>
      <ShortName>Loans - Troubled Debt Restructurings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>40701 - Disclosure - Allowance For Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureAllowanceForLoanLossesDetails</Role>
      <ShortName>Allowance For Loan Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureAllowanceForLoanLossesTables</ParentRole>
      <Position>70</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>40801 - Disclosure - Premises and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosurePremisesAndEquipmentDetails</Role>
      <ShortName>Premises and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosurePremisesAndEquipmentTables</ParentRole>
      <Position>71</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>40901 - Disclosure - Goodwill and Core Deposit Intangibles (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureGoodwillAndCoreDepositIntangiblesDetails</Role>
      <ShortName>Goodwill and Core Deposit Intangibles (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureGoodwillAndCoreDepositIntangiblesTables</ParentRole>
      <Position>72</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>41001 - Disclosure - Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDepositsDetails</Role>
      <ShortName>Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureDepositsTables</ParentRole>
      <Position>73</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>41101 - Disclosure - Securities sold under agreements to repurchase and Other Borrowed Funds (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSecuritiesSoldUnderAgreementsToRepurchaseAndOtherBorrowedFundsDetails</Role>
      <ShortName>Securities sold under agreements to repurchase and Other Borrowed Funds (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureSecuritiesSoldUnderAgreementsToRepurchaseAndOtherBorrowedFundsTables</ParentRole>
      <Position>74</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>41201 - Disclosure - Subordinated Debentures and Subordinated Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSubordinatedDebenturesAndSubordinatedNotesDetails</Role>
      <ShortName>Subordinated Debentures and Subordinated Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureSubordinatedDebenturesAndSubordinatedNotesTables</ParentRole>
      <Position>75</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>41301 - Disclosure - Income Taxes - Components (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureIncomeTaxesComponentsDetails</Role>
      <ShortName>Income Taxes - Components (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>41302 - Disclosure - Income Taxes - Tax Rate Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureIncomeTaxesTaxRateReconciliationDetails</Role>
      <ShortName>Income Taxes - Tax Rate Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>41303 - Disclosure - Income Taxes - Deferred Tax Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureIncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails</Role>
      <ShortName>Income Taxes - Deferred Tax Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>41304 - Disclosure - Income Taxes - Net Operating Loss Carryforwards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureIncomeTaxesNetOperatingLossCarryforwardsDetails</Role>
      <ShortName>Income Taxes - Net Operating Loss Carryforwards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>41401 - Disclosure - Employee Benefits - Equity Incentive Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefitsEquityIncentivePlansDetails</Role>
      <ShortName>Employee Benefits - Equity Incentive Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>41402 - Disclosure - Employee Benefits - Black-Scholes Fair Value Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefitsBlackScholesFairValueAssumptionsDetails</Role>
      <ShortName>Employee Benefits - Black-Scholes Fair Value Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>41403 - Disclosure - Employee Benefits - Options Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefitsOptionsActivityDetails</Role>
      <ShortName>Employee Benefits - Options Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>41404 - Disclosure - Employee Benefits - Nonvested Options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefitsNonvestedOptionsDetails</Role>
      <ShortName>Employee Benefits - Nonvested Options (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>41405 - Disclosure - Employee Benefits - Compensation Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefitsCompensationCostsDetails</Role>
      <ShortName>Employee Benefits - Compensation Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>41407 - Disclosure - Employee Benefits - Stock Appreciation Rights Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefitsStockAppreciationRightsPlanDetails</Role>
      <ShortName>Employee Benefits - Stock Appreciation Rights Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>41408 - Disclosure - Employee Benefits - Benefit Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureEmployeeBenefitsBenefitPlanDetails</Role>
      <ShortName>Employee Benefits - Benefit Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>41501 - Disclosure - Off-Balance Sheet Arrangements, Commitments And Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndContingenciesDetails</Role>
      <ShortName>Off-Balance Sheet Arrangements, Commitments And Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndContingenciesTables</ParentRole>
      <Position>87</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>41502 - Disclosure - Off-Balance Sheet Arrangements, Commitments And Contingencies - Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndContingenciesLeasesDetails</Role>
      <ShortName>Off-Balance Sheet Arrangements, Commitments And Contingencies - Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndContingenciesTables</ParentRole>
      <Position>88</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>41503 - Disclosure - Off-Balance Sheet Arrangements, Commitments And Contingencies - Litigation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndContingenciesLitigationDetails</Role>
      <ShortName>Off-Balance Sheet Arrangements, Commitments And Contingencies - Litigation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsAndContingenciesTables</ParentRole>
      <Position>89</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>41601 - Disclosure - Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDerivativeFinancialInstrumentsDetails</Role>
      <ShortName>Derivative Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureDerivativeFinancialInstrumentsTables</ParentRole>
      <Position>90</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>41602 - Disclosure - Derivative Financial Instruments - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDerivativeFinancialInstrumentsAdditionalInformationDetails</Role>
      <ShortName>Derivative Financial Instruments - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>41701 - Disclosure - Regulatory Matters (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureRegulatoryMattersDetails</Role>
      <ShortName>Regulatory Matters (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureRegulatoryMattersTables</ParentRole>
      <Position>92</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>41801 - Disclosure - Disclosures About Fair Value of Financial Instruments - Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDisclosuresAboutFairValueOfFinancialInstrumentsRecurringBasisDetails</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>41802 - Disclosure - Disclosures About Fair Value of Financial Instruments - Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDisclosuresAboutFairValueOfFinancialInstrumentsNonrecurringBasisDetails</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Nonrecurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>41803 - Disclosure - Disclosures About Fair Value of Financial Instruments - Balance Sheet Grouping (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureDisclosuresAboutFairValueOfFinancialInstrumentsBalanceSheetGroupingDetails</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Balance Sheet Grouping (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>41901 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureSubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.greenbank.com/role/DisclosureSubsequentEvents</ParentRole>
      <Position>96</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>42001 - Disclosure - Parent Company Only Financial Statements - Condensed Balance Sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureParentCompanyOnlyFinancialStatementsCondensedBalanceSheetsDetails</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed Balance Sheets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>42002 - Disclosure - Parent Company Only Financial Statements - Condensed Statements of Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureParentCompanyOnlyFinancialStatementsCondensedStatementsOfOperationsDetails</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed Statements of Operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>42003 - Disclosure - Parent Company Only Financial Statements - Condensed Statements of Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureParentCompanyOnlyFinancialStatementsCondensedStatementsOfComprehensiveIncomeDetails</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed Statements of Comprehensive Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="gnbc-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>42004 - Disclosure - Parent Company Only Financial Statements - Condensed Statements of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.greenbank.com/role/DisclosureParentCompanyOnlyFinancialStatementsCondensedStatementsOfCashFlowsDetails</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed Statements of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>gnbc-20161231.xml</File>
    <File>gnbc-20161231.xsd</File>
    <File>gnbc-20161231_cal.xml</File>
    <File>gnbc-20161231_def.xml</File>
    <File>gnbc-20161231_lab.xml</File>
    <File>gnbc-20161231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
