Prospectus: Document Type Period End Date Document Period End Date Registrant Name CIK Entity Central Index Key Amendment Flag Document Creation Date Document Effective Date Prospectus Date Legal Entity Identifier Entity Inv Company Type Amendment Description Trading Symbol Net Expenses (as a percentage of Assets) Net Expenses Expenses (as a percentage of Assets) Total Annual Fund Operating Expenses[ctag:span_t-indent1-rule3] Total Annual Fund Operating Expenses[ctag:span_t-indent1-rule3] Management Fees (as a percentage of Assets) Management Fees[ctag:span_t-indent1] Distribution and Service (12b-1) Fees Distribution and Service (12b-1) Fees[ctag:span_t-indent1] Distribution or Similar (Non 12b-1) Fees Other Expenses (as a percentage of Assets): Other Expenses Other Expenses[ctag:span_t-indent1-rule] Other Expenses[ctag:span_t-indent1] Component1 Other Expenses Component2 Other Expenses Component3 Other Expenses Acquired Fund Fees and Expenses Acquired Fund Fees and Expenses[ctag:span_t-indent1-rule] Fee Waiver or Reimbursement Fee Waiver or Reimbursement Performance Measure [Axis] Share Class [Axis] Document [Axis] Prospectus Coregistrant [Axis] Coregistrant [Domain] Series [Axis] Series S000057894 [Member] First Trust California Municipal High Income ETF First Trust California Municipal High Income ETF Member Before Taxes After Taxes on Distributions After Taxes on Distributions and Sales Aftertaxondistributions [Member] Aftertaxondistributions Member After tax on distributions Aftertaxondistributionsandsaleoffundshares [Member] Aftertaxondistributionsandsaleoffundshares Member After tax on distributions and sale of fund shares Bloomberg Ten Year California Exempt Index [Member] Bloomberg Ten Year California Exempt Index Member Bloomberg 10 Year California Exempt Index (reflects no deduction for fees, expenses or taxes) Bloomberg Municipal Bond Index [Member] Bloomberg Municipal Bond Index Member Bloomberg Municipal Bond Index (reflects no deduction for fees, expenses or taxes) Share Classes C000187865 [Member] First Trust California Municipal High Income ETF First Trust California Municipal High Income ETF Risk [Axis] All Risks [Member] Risk Nondiversified Status [Member] Risk Lose Money [Member] Risk Money Market Fund Price Fluctuates [Member] Risk Money Market Fund May Impose Fees or Suspend Sales [Member] Risk Money Market Fund May Not Preserve Dollar [Member] Risk Money Market Fund Sponsor May Not Provide Support [Member] Risk Not Insured Depository Institution [Member] Risk Not Insured [Member] Alternative Minimum Tax Risk [Member] Alternative Minimum Tax Risk [Member] Authorized Participant Concentration Risk [Member] Authorized Participant Concentration Risk [Member] California Municipal Securities Risk [Member] California Municipal Securities Risk [Member] Call Risk [Member] Call Risk [Member] Cash Transactions Risk [Member] Cash Transactions Risk [Member] Counterparty Risk [Member] Counterparty Risk [Member] Credit Rating Agency Risk [Member] Credit Rating Agency Risk [Member] Credit Risk [Member] Credit Risk [Member] Credit Spread Risk [Member] Credit Spread Risk [Member] Current Market Conditions Risk [Member] Current Market Conditions Risk [Member] Cyber Security Risk [Member] Cyber Security Risk [Member] Debt Securities Risk [Member] Debt Securities Risk [Member] Derivatives Risk [Member] Derivatives Risk [Member] Distressed Securities Risk [Member] Distressed Securities Risk [Member] Extension Risk [Member] Extension Risk [Member] Futures Contracts Risk [Member] Futures Contracts Risk [Member] High Yield Securities Risk [Member] High Yield Securities Risk [Member] Income Risk [Member] Income Risk [Member] Index Or Model Constituent Risk [Member] Index Or Model Constituent Risk [Member] Industrial Development Bond Risk [Member] Industrial Development Bond Risk [Member] Inflation Risk [Member] Inflation Risk [Member] Interest Rate Risk [Member] Interest Rate Risk [Member] Leverage Risk [Member] Leverage Risk [Member] Liquidity Risk [Member] Liquidity Risk [Member] Management Risk [Member] Management Risk [Member] Market Maker Risk [Member] Market Maker Risk [Member] Market Risk [Member] Market Risk [Member] Municipal Securities Market Liquidity Risk [Member] Municipal Securities Market Liquidity Risk [Member] Municipal Securities Risk [Member] Municipal Securities Risk [Member] Operational Risk [Member] Operational Risk [Member] Premium Discount Risk [Member] Premium Discount Risk [Member] Prepayment Risk [Member] Prepayment Risk [Member] Pre Refunded Bonds Risk [Member] Pre Refunded Bonds Risk [Member] Private Activity Bonds Risk [Member] Private Activity Bonds Risk [Member] Significant Exposure Risk [Member] Significant Exposure Risk [Member] State Specific And Us Territories? Concentration Risk [Member] State Specific And Us Territories? Concentration Risk [Member] Trading Issues Risk [Member] Trading Issues Risk [Member] Valuation Risk [Member] Valuation Risk [Member] Volatility Risk [Member] Volatility Risk [Member] Risk/Return [Heading] Objective [Heading] Objective, Primary [Text Block] Expense [Heading] Expense Narrative [Text Block] Shareholder Fees Caption [Text] Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)[ctag:span_t-rule1] Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Operating Expenses Caption [Text] Portfolio Turnover [Heading] Portfolio Turnover [Text Block] Portfolio Turnover, Rate Expense Example [Heading] Expense Example, No Redemption Narrative [Text Block] 1 Year Expense Example, No Redemption, 1 Year 3 Years Expense Example, No Redemption, 3 Years 5 Years Expense Example, No Redemption, 5 Years 10 Years Expense Example, No Redemption, 10 Years Strategy [Heading] Strategy Narrative [Text Block] Strategy Portfolio Concentration [Text] Risk [Heading] Risk [Text Block] Risk Caption Bar Chart and Performance Table [Heading] Performance Narrative [Text Block] Performance Information Illustrates Variability of Returns [Text] Performance Availability Website Address [Text] Performance Past Does Not Indicate Future [Text] Bar Chart [Heading] 2018 Annual Return 2018 2019 Annual Return 2019 2020 Annual Return 2020 2021 Annual Return 2021 2022 Annual Return 2022 2023 Annual Return 2023 Bar Chart Footnotes [Text Block] Bar Chart Closing [Text Block] Year to Date Return, Label Bar Chart, Year to Date Return, Date Bar Chart, Year to Date Return Highest Quarterly Return, Label Highest Quarterly Return, Date Highest Quarterly Return Lowest Quarterly Return, Label Lowest Quarterly Return, Date Lowest Quarterly Return Performance Table Heading Performance Table Uses Highest Federal Rate Performance Table Not Relevant to Tax Deferred Performance Table Explanation after Tax Higher Performance Table Narrative 1 Year 5 Years Since Inception Inception Date Objective, Secondary [Text Block] Shareholder Fees Column [Text] Maximum Cumulative Sales Charge (as a percentage of Offering Price) Maximum Cumulative Sales Charge (as a percentage) Maximum Deferred Sales Charge (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage) Maximum Sales Charge on Reinvested Dividends and Distributions (as a percentage) Redemption Fee (as a percentage of Amount Redeemed) Redemption Fee (as a percentage of Amount Redeemed) Redemption Fee Redemption Fee Exchange Fee (as a percentage of Amount Redeemed) Exchange Fee Maximum Account Fee (as a percentage of Assets) Maximum Account Fee Shareholder Fee, Other Operating Expenses Column [Text] Fee Waiver or Reimbursement over Assets, Date of Termination Expense Footnotes [Text Block] Expenses Deferred Charges [Text Block] Expenses Range of Exchange Fees [Text Block] Expense Breakpoint Discounts [Text] Expense Breakpoint, Minimum Investment Required [Amount] Expenses Represent Both Master and Feeder [Text] Expenses Explanation of Nonrecurring Account Fee [Text] Other Expenses, New Fund, Based on Estimates [Text] Acquired Fund Fees and Expenses, Based on Estimates [Text] Expenses Other Expenses Had Extraordinary Expenses Been Included [Text] Expenses Restated to Reflect Current [Text] Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] Expense Example by Year [Heading] Expense Example Narrative [Text Block] Expense Example by, Year, Caption [Text] Expense Example, with Redemption, 1 Year 1 Year Expense Example, with Redemption, 3 Years 3 Years Expense Example, with Redemption, 5 Years 5 Years Expense Example, with Redemption, 10 Years 10 Years Expense Example, No Redemption, By Year, Caption [Text] Expense Example Footnotes [Text Block] Expense Example Closing [Text Block] Risk Footnotes [Text Block] Risk Closing [Text Block] Risk Column [Text] Performance One Year or Less [Text] Performance Additional Market Index [Text] Performance Availability Phone [Text] Bar Chart Narrative [Text Block] Bar Chart Does Not Reflect Sales Loads [Text] Annual Return Caption [Text] Caption Annual Return, Column [Text] Column Annual Return, Inception Date Inception Date Annual Return 1990 Annual Return 1991 Annual Return 1992 Annual Return 1993 Annual Return 1994 Annual Return 1995 Annual Return 1996 Annual Return 1997 Annual Return 1998 Annual Return 1999 Annual Return 2000 Annual Return 2001 Annual Return 2002 Annual Return 2003 Annual Return 2004 Annual Return 2005 Annual Return 2006 Annual Return 2007 Annual Return 2008 Annual Return 2009 Annual Return 2010 Annual Return 2011 Annual Return 2012 Annual Return 2013 Annual Return 2014 Annual Return 2015 Annual Return 2016 Annual Return 2017 2017 Annual Return 2024 Annual Return 2025 Bar Chart, Reason Selected Class Different from Immediately Preceding Period [Text] Bar Chart, Returns for Class Not Offered in Prospectus [Text] Performance Table Does Reflect Sales Loads Performance Table Market Index Changed Index No Deduction for Fees, Expenses, Taxes [Text] Performance Table One Class of after Tax Shown [Text] Performance Table Footnotes, Reason Performance Information for Class Different from Immediately Preceding Period [Text] Performance Table Footnotes Performance Table Closing [Text Block] Average Annual Return, Caption Average Annual Return, Column Name Label 10 Years Money Market Seven Day Yield, Caption [Text] Money Market Seven Day Yield Column [Text] Money Market Seven Day Yield Phone Money Market Seven Day Yield Money Market Seven Day Tax Equivalent Yield Thirty Day Yield Caption Thirty Day Yield Column [Text] Thirty Day Yield Phone Thirty Day Yield Thirty Day Tax Equivalent Yield Supplement to Prospectus [Text Block] S000054960 [Member] First Trust Horizon Managed Volatility Domestic ETF First Trust Horizon Managed Volatility Domestic ETF Member S P Five Hundred Index [Member] S P Five Hundred Index Member S&P 500® Index (reflects no 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Asia Risk [Member] Currency Risk [Member] Currency Risk [Member] Depositary Receipts Risk [Member] Depositary Receipts Risk [Member] Europe Risk [Member] Europe Risk [Member] Financial Companies Risk [Member] Financial Companies Risk [Member] Mid Capitalization Companies Risk [Member] Mid Capitalization Companies Risk [Member] Non US Securities Risk [Member] Non US Securities Risk [Member] S000068212 [Member] First Trust Horizon Managed Volatility Small Mid ETF First Trust Horizon Managed Volatility Small Mid ETF Member S P One Thousand Index [Member] S P One Thousand Index Member S&P 1000® Index (reflects no deduction for fees, expenses or taxes) Russell Three Thousand Index [Member] Russell Three Thousand Index Member Russell 3000® Index (reflects no deduction for fees, expenses or taxes) C000218390 [Member] First Trust Horizon Managed Volatility Small/Mid ETF First Trust Horizon Managed Volatility Small/Mid ETF Market Capitalization Deviation Risk [Member] Market Capitalization 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Duration Managed Municipal ETF Member Bloomberg Municipal Short One Five Year Index [Member] Bloomberg Municipal Short One Five Year Index Member Bloomberg Municipal Short (1-5) Year Index (reflects no deduction for fees, expenses or taxes) C000205581 [Member] First Trust Short Duration Managed Municipal ETF First Trust Short Duration Managed Municipal ETF Floating Rate Debt Instruments Risk [Member] Floating Rate Debt Instruments Risk [Member] When Issued TBA And Delayed Delivery Transactions Risk [Member] When Issued TBA And Delayed Delivery Transactions Risk [Member] S000063443 [Member] First Trust Ultra Short Duration Municipal ETF First Trust Ultra Short Duration Municipal ETF Member Bloomberg Municipal Short Term Index [Member] Bloomberg Municipal Short Term Index Member Bloomberg Municipal Short-Term Index (reflects no deduction for fees, expenses or taxes) C000205579 [Member] First Trust Ultra Short Duration Municipal ETF First Trust Ultra Short Duration Municipal ETF When Issued and Delayed Delivery Transactions Risk [Member] When Issued and Delayed Delivery Transactions Risk [Member]