<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>163</ContextCount>
  <ElementCount>420</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>59</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>9</UnitCount>
  <MyReports>
    <Report instance="aplt-20191231.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.appliedtherapeutics.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementBalanceSheets</Role>
      <ShortName>Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementBalanceSheetsParenthetical</Role>
      <ShortName>Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - Statements of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementStatementsOfOperations</Role>
      <ShortName>Statements of Operations</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - Statements of Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementStatementsOfComprehensiveIncomeLoss</Role>
      <ShortName>Statements of Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - Statement of Convertible Preferred Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementStatementOfConvertiblePreferredStock</Role>
      <ShortName>Statement of Convertible Preferred Stock</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00405 - Statement - Statement of Convertible Preferred Stock (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementStatementOfConvertiblePreferredStockParenthetical</Role>
      <ShortName>Statement of Convertible Preferred Stock (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>00410 - Statement - Condensed Statement of Stockholders' (Deficit) Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementCondensedStatementOfStockholdersDeficitEquity</Role>
      <ShortName>Condensed Statement of Stockholders' (Deficit) Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>00415 - Statement - Statement of Stockholders' (Deficit) Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementStatementOfStockholdersDeficitEquityParenthetical</Role>
      <ShortName>Statement of Stockholders' (Deficit) Equity (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>00500 - Statement - Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementStatementsOfCashFlows</Role>
      <ShortName>Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>00505 - Statement - Statements of Cash Flows (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/StatementStatementsOfCashFlowsParenthetical</Role>
      <ShortName>Statements of Cash Flows (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10101 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10201 - Disclosure - LICENSE AGREEMENT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureLicenseAgreement</Role>
      <ShortName>LICENSE AGREEMENT</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10301 - Disclosure - FAIR VALUE MEASUREMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>FAIR VALUE MEASUREMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10401 - Disclosure - INVESTMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureInvestments</Role>
      <ShortName>INVESTMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10501 - Disclosure - CONVERTIBLE PROMISSORY NOTES</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureConvertiblePromissoryNotes</Role>
      <ShortName>CONVERTIBLE PROMISSORY NOTES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>10601 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssets</Role>
      <ShortName>PREPAID EXPENSES AND OTHER CURRENT ASSETS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>10701 - Disclosure - ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilities</Role>
      <ShortName>ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>10801 - Disclosure - STOCK BASED COMPENSATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensation</Role>
      <ShortName>STOCK BASED COMPENSATION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>10901 - Disclosure - STOCKHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockholdersEquity</Role>
      <ShortName>STOCKHOLDERS' EQUITY</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11001 - Disclosure - WARRANTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureWarrants</Role>
      <ShortName>WARRANTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11101 - Disclosure - LEASES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureLeases</Role>
      <ShortName>LEASES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11201 - Disclosure - INCOME TAXES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>INCOME TAXES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11301 - Disclosure - BENEFIT PLANS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureBenefitPlans</Role>
      <ShortName>BENEFIT PLANS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>11401 - Disclosure - NET LOSS PER COMMON SHARE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureNetLossPerCommonShare</Role>
      <ShortName>NET LOSS PER COMMON SHARE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>11501 - Disclosure - RELATED PARTIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureRelatedParties</Role>
      <ShortName>RELATED PARTIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>11601 - Disclosure - SUBSEQUENT EVENT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureSubsequentEvent</Role>
      <ShortName>SUBSEQUENT EVENT</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>20102 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>30303 - Disclosure - FAIR VALUE MEASUREMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>FAIR VALUE MEASUREMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>30403 - Disclosure - INVESTMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureInvestmentsTables</Role>
      <ShortName>INVESTMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureInvestments</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>30603 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</Role>
      <ShortName>PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssets</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>30703 - Disclosure - ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesTables</Role>
      <ShortName>ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilities</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>30803 - Disclosure - STOCK BASED COMPENSATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensationTables</Role>
      <ShortName>STOCK BASED COMPENSATION (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensation</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>30903 - Disclosure - STOCKHOLDER EQUITY (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockholderEquityTables</Role>
      <ShortName>STOCKHOLDER EQUITY (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>31003 - Disclosure - WARRANTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureWarrantsTables</Role>
      <ShortName>WARRANTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureWarrants</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>31103 - Disclosure - LEASES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureLeasesTables</Role>
      <ShortName>LEASES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureLeases</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>31203 - Disclosure - INCOME TAXES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>INCOME TAXES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureIncomeTaxes</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>31403 - Disclosure - NET LOSS PER COMMON SHARE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureNetLossPerCommonShareTables</Role>
      <ShortName>NET LOSS PER COMMON SHARE (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureNetLossPerCommonShare</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>40101 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock issued (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPoliciesStockIssuedDetails</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock issued (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>40102 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred Offering Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPoliciesDeferredOfferingCostsDetails</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred Offering Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>40103 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock-based compensation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPoliciesStockBasedCompensationDetails</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock-based compensation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>40104 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPoliciesIncomeTaxesDetails</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>40105 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recently Adopted Accounting Pronouncements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPoliciesRecentlyAdoptedAccountingPronouncementsDetails</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recently Adopted Accounting Pronouncements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>40106 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPoliciesLeasesDetails</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureOrganizationAndSummaryOfSignificantAccountingPoliciesPolicies</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>40201 - Disclosure - LICENSE AGREEMENT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureLicenseAgreementDetails</Role>
      <ShortName>LICENSE AGREEMENT (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureLicenseAgreement</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>40301 - Disclosure - FAIR VALUE MEASUREMENTS - FV hierarchy (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureFairValueMeasurementsFvHierarchyDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENTS - FV hierarchy (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>40302 - Disclosure - FAIR VALUE MEASUREMENTS - Transfers (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureFairValueMeasurementsTransfersDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENTS - Transfers (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>40303 - Disclosure - FAIR VALUE MEASUREMENTS - Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureFairValueMeasurementsAssumptionsDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENTS - Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>40304 - Disclosure - FAIR VALUE MEASUREMENTS - Level 3 roll forward (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureFairValueMeasurementsLevel3RollForwardDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENTS - Level 3 roll forward (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>40401 - Disclosure - INVESTMENTS - By type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureInvestmentsByTypeDetails</Role>
      <ShortName>INVESTMENTS - By type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>40402 - Disclosure - INVESTMENTS - By contractual maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureInvestmentsByContractualMaturityDetails</Role>
      <ShortName>INVESTMENTS - By contractual maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>40501 - Disclosure - CONVERTIBLE PROMISSORY NOTES (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureConvertiblePromissoryNotesDetails</Role>
      <ShortName>CONVERTIBLE PROMISSORY NOTES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureConvertiblePromissoryNotes</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>40601 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsDetails</Role>
      <ShortName>PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>40701 - Disclosure - ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesDetails</Role>
      <ShortName>ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesTables</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>40801 - Disclosure - STOCK BASED COMPENSATION - Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensationPlansDetails</Role>
      <ShortName>STOCK BASED COMPENSATION - Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>40802 - Disclosure - STOCK BASED COMPENSATION - Stock-based compensation expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensationStockBasedCompensationExpenseDetails</Role>
      <ShortName>STOCK BASED COMPENSATION - Stock-based compensation expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>40803 - Disclosure - STOCK BASED COMPENSATION - Options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensationOptionsDetails</Role>
      <ShortName>STOCK BASED COMPENSATION - Options (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>40804 - Disclosure - STOCK BASED COMPENSATION - Options outstanding (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensationOptionsOutstandingDetails</Role>
      <ShortName>STOCK BASED COMPENSATION - Options outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>40805 - Disclosure - STOCK BASED COMPENSATION - Options that Contain Service, Performance and Market Conditions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensationOptionsThatContainServicePerformanceAndMarketConditionsDetails</Role>
      <ShortName>STOCK BASED COMPENSATION - Options that Contain Service, Performance and Market Conditions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>40806 - Disclosure - STOCK BASED COMPENSATION - Valuation assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensationValuationAssumptionsDetails</Role>
      <ShortName>STOCK BASED COMPENSATION - Valuation assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>40807 - Disclosure - STOCK BASED COMPENSATION - Service, Performance and Market Condition Option Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensationServicePerformanceAndMarketConditionOptionInformationDetails</Role>
      <ShortName>STOCK BASED COMPENSATION - Service, Performance and Market Condition Option Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>40808 - Disclosure - STOCK BASED COMPENSATION - 2019 Employee Stock Purchase Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockBasedCompensation2019EmployeeStockPurchasePlanDetails</Role>
      <ShortName>STOCK BASED COMPENSATION - 2019 Employee Stock Purchase Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>40901 - Disclosure - STOCKHOLDERS' EQUITY - Authorized, issued and outstanding and Common Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockholdersEquityAuthorizedIssuedAndOutstandingAndCommonStockDetails</Role>
      <ShortName>STOCKHOLDERS' EQUITY - Authorized, issued and outstanding and Common Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>40902 - Disclosure - STOCKHOLDERS' EQUITY - Preferred stock issued (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockholdersEquityPreferredStockIssuedDetails</Role>
      <ShortName>STOCKHOLDERS' EQUITY - Preferred stock issued (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>40903 - Disclosure - STOCKHOLDERS' EQUITY - Preferred stock summary (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockholdersEquityPreferredStockSummaryDetails</Role>
      <ShortName>STOCKHOLDERS' EQUITY - Preferred stock summary (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>40904 - Disclosure - STOCKHOLDERS' EQUITY - Preferred stock other information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureStockholdersEquityPreferredStockOtherInformationDetails</Role>
      <ShortName>STOCKHOLDERS' EQUITY - Preferred stock other information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>41001 - Disclosure - WARRANTS - Issued with Series A Preferred Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureWarrantsIssuedWithSeriesPreferredStockDetails</Role>
      <ShortName>WARRANTS - Issued with Series A Preferred Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>41002 - Disclosure - WARRANTS - 2017 Warrants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureWarrants2017WarrantsDetails</Role>
      <ShortName>WARRANTS - 2017 Warrants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>41003 - Disclosure - WARRANTS - Issued with the 2018 Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureWarrantsIssuedWith2018NotesDetails</Role>
      <ShortName>WARRANTS - Issued with the 2018 Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>41004 - Disclosure - WARRANTS - Issued with Series B Preferred Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureWarrantsIssuedWithSeriesBPreferredStockDetails</Role>
      <ShortName>WARRANTS - Issued with Series B Preferred Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>41005 - Disclosure - WARRANTS - 2018 Warrants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureWarrants2018WarrantsDetails</Role>
      <ShortName>WARRANTS - 2018 Warrants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>41101 - Disclosure - LEASES - ROU Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureLeasesRouAssetsAndLiabilitiesDetails</Role>
      <ShortName>LEASES - ROU Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>41102 - Disclosure - LEASES - Lease Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureLeasesLeaseCostDetails</Role>
      <ShortName>LEASES - Lease Cost (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>41103 - Disclosure - LEASES - Supplemental Cash Flow Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureLeasesSupplementalCashFlowInformationDetails</Role>
      <ShortName>LEASES - Supplemental Cash Flow Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>41104 - Disclosure - LEASES - Maturities of Lease Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureLeasesMaturitiesOfLeaseLiabilitiesDetails</Role>
      <ShortName>LEASES - Maturities of Lease Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>41201 - Disclosure - INCOME TAXES - Provision (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureIncomeTaxesProvisionDetails</Role>
      <ShortName>INCOME TAXES - Provision (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>41202 - Disclosure - INCOME TAXES - Deferred taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureIncomeTaxesDeferredTaxesDetails</Role>
      <ShortName>INCOME TAXES - Deferred taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>41203 - Disclosure - INCOME TAXES - NOLs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureIncomeTaxesNolsDetails</Role>
      <ShortName>INCOME TAXES - NOLs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>41204 - Disclosure - INCOME TAXES - Income tax rate reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureIncomeTaxesIncomeTaxRateReconciliationDetails</Role>
      <ShortName>INCOME TAXES - Income tax rate reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>41301 - Disclosure - BENEFIT PLANS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureBenefitPlansDetails</Role>
      <ShortName>BENEFIT PLANS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureBenefitPlans</ParentRole>
      <Position>80</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>41401 - Disclosure - NET LOSS PER COMMON SHARE - EPS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureNetLossPerCommonShareEpsDetails</Role>
      <ShortName>NET LOSS PER COMMON SHARE - EPS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureNetLossPerCommonShareTables</ParentRole>
      <Position>81</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>41402 - Disclosure - NET LOSS PER COMMON SHARE - Anti-dilutive securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureNetLossPerCommonShareAntiDilutiveSecuritiesDetails</Role>
      <ShortName>NET LOSS PER COMMON SHARE - Anti-dilutive securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>41501 - Disclosure - RELATED PARTIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureRelatedPartiesDetails</Role>
      <ShortName>RELATED PARTIES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureRelatedParties</ParentRole>
      <Position>83</Position>
    </Report>
    <Report instance="aplt-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>41601 - Disclosure - SUBSEQUENT EVENT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.appliedtherapeutics.com/role/DisclosureSubsequentEventDetails</Role>
      <ShortName>SUBSEQUENT EVENT (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.appliedtherapeutics.com/role/DisclosureSubsequentEvent</ParentRole>
      <Position>84</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>aplt-20191231.xml</File>
    <File>aplt-20191231.xsd</File>
    <File>aplt-20191231_cal.xml</File>
    <File>aplt-20191231_def.xml</File>
    <File>aplt-20191231_lab.xml</File>
    <File>aplt-20191231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
