<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.19.3</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>80</ContextCount>
  <ElementCount>235</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>19</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000100 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>010000 - Statement - CONDENSED BALANCE SHEET (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/CondensedBalanceSheetUnaudited</Role>
      <ShortName>CONDENSED BALANCE SHEET (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>010100 - Statement - CONDENSED BALANCE SHEET (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/CondensedBalanceSheetUnauditedParenthetical</Role>
      <ShortName>CONDENSED BALANCE SHEET (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>020000 - Statement - CONDENSED STATEMENTS OF OPERATIONS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/CondensedStatementsOfOperationsUnaudited</Role>
      <ShortName>CONDENSED STATEMENTS OF OPERATIONS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>020100 - Statement - CONDENSED STATEMENTS OF OPERATIONS (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/CondensedStatementsOfOperationsUnauditedParenthetical</Role>
      <ShortName>CONDENSED STATEMENTS OF OPERATIONS (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>030000 - Statement - CONDENSED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/CondensedStatementOfChangesInStockholdersEquityUnaudited</Role>
      <ShortName>CONDENSED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>030100 - Statement - CONDENSED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/CondensedStatementOfChangesInStockholdersEquityUnauditedParenthetical</Role>
      <ShortName>CONDENSED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>040000 - Statement - CONDENSED STATEMENT OF CASH FLOWS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/CondensedStatementOfCashFlowsUnaudited</Role>
      <ShortName>CONDENSED STATEMENT OF CASH FLOWS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>060100 - Disclosure - Description of Organization and Business Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/DescriptionOfOrganizationAndBusinessOperations</Role>
      <ShortName>Description of Organization and Business Operations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>060200 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/SummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>060300 - Disclosure - Initial Public Offering</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/InitialPublicOffering</Role>
      <ShortName>Initial Public Offering</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>060400 - Disclosure - Private Placement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/PrivatePlacement</Role>
      <ShortName>Private Placement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>060500 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/RelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>060600 - Disclosure - Commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/Commitments</Role>
      <ShortName>Commitments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>060700 - Disclosure - Stockholder's Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/StockholderSEquity</Role>
      <ShortName>Stockholder's Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>060800 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>060900 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>070200 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/SummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>18</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>080200 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/SummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>19</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>080800 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/FairValueMeasurements</ParentRole>
      <Position>20</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>090100 - Disclosure - Description of Organization and Business Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/DescriptionOfOrganizationAndBusinessOperationsDetails</Role>
      <ShortName>Description of Organization and Business Operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/DescriptionOfOrganizationAndBusinessOperations</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>090200 - Disclosure - Summary of Significant Accounting Policies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/SummaryOfSignificantAccountingPoliciesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/SummaryOfSignificantAccountingPoliciesTables</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>090300 - Disclosure - Initial Public Offering (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/InitialPublicOfferingDetails</Role>
      <ShortName>Initial Public Offering (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/InitialPublicOffering</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>090400 - Disclosure - Private Placement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/PrivatePlacementDetails</Role>
      <ShortName>Private Placement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/PrivatePlacement</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>090500 - Disclosure - Related Party Transactions, Founder Shares (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/RelatedPartyTransactionsFounderSharesDetails</Role>
      <ShortName>Related Party Transactions, Founder Shares (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>090502 - Disclosure - Related Party Transactions, Promissory Note, Administrative Support Agreement and Related Party Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/RelatedPartyTransactionsPromissoryNoteAdministrativeSupportAgreementAndRelatedPartyLoansDetails</Role>
      <ShortName>Related Party Transactions, Promissory Note, Administrative Support Agreement and Related Party Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>090600 - Disclosure - Commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/CommitmentsDetails</Role>
      <ShortName>Commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/Commitments</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>090700 - Disclosure - Stockholder's Equity, Preferred Stock and Common Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/StockholderSEquityPreferredStockAndCommonStockDetails</Role>
      <ShortName>Stockholder's Equity, Preferred Stock and Common Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>090702 - Disclosure - Stockholder's Equity, Warrants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/StockholderSEquityWarrantsDetails</Role>
      <ShortName>Stockholder's Equity, Warrants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="smmc-20190930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>090800 - Disclosure - Fair Value Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://smmergercorp.com/role/FairValueMeasurementsDetails</Role>
      <ShortName>Fair Value Measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://smmergercorp.com/role/FairValueMeasurementsTables</ParentRole>
      <Position>30</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>smmc-20190930.xml</File>
    <File>smmc-20190930.xsd</File>
    <File>smmc-20190930_cal.xml</File>
    <File>smmc-20190930_def.xml</File>
    <File>smmc-20190930_lab.xml</File>
    <File>smmc-20190930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
