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 Annual Fund Operating Expenses[ctag:span_t-indent1-rule3] Net Annual Fund Operating Expenses[ctag:span_t-indent1-rule3] 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 and Expense Reimbursement[ctag:span_t-indent1-rule] Performance Measure [Axis] Share Class [Axis] Document [Axis] Prospectus Coregistrant [Axis] Coregistrant [Domain] Series [Axis] Series S000017696 [Member] First Trust Consumer Discretionary AlphaDEX Fund First Trust Consumer Discretionary AlphaDEX Fund 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 Strata Quant Consumer Discretionary Index [Member] Strata Quant Consumer Discretionary Index Member StrataQuant® Consumer Discretionary Index (reflects no deduction for fees, expenses or taxes) Russell One Thousand Index [Member] Russell One Thousand Index Member Russell 1000® Index (reflects no deduction for fees, expenses or taxes) S P Five Hundred Consumer Discretionary Index [Member] S P Five Hundred Consumer Discretionary Index Member S&P 500® Consumer Discretionary Index (reflects no deduction for fees, expenses or taxes) Russell One Thousand Consumer Discretionary Index [Member] Russell One Thousand Consumer Discretionary Index Member Russell 1000® Consumer Discretionary 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) Share Classes C000048896 [Member] First Trust Consumer Discretionary AlphaDEX Fund First Trust Consumer Discretionary AlphaDEX Fund 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] Authorized Participant Concentration Risk [Member] Authorized Participant Concentration Risk [Member] Consumer Discretionary Companies Risk [Member] Consumer Discretionary Companies Risk [Member] Current Market Conditions Risk [Member] Current Market Conditions Risk [Member] Cyber Security Risk [Member] Cyber Security Risk [Member] Equity Securities Risk [Member] Equity Securities Risk [Member] Growth Stocks Investment Risk [Member] Growth Stocks Investment Risk [Member] Index Concentration Risk [Member] Index Concentration Risk [Member] Index Or Model Constituent Risk [Member] Index Or Model Constituent Risk [Member] Index Provider Risk [Member] Index Provider Risk [Member] Market Maker Risk [Member] Market Maker Risk [Member] Market Risk [Member] Market Risk [Member] Non Correlation Risk [Member] Non Correlation Risk [Member] Operational Risk [Member] Operational Risk [Member] Passive Investment Risk [Member] Passive Investment Risk [Member] Portfolio Turnover Risk [Member] Portfolio Turnover Risk [Member] Premium Discount Risk [Member] Premium Discount Risk [Member] Smaller Companies Risk [Member] Smaller Companies Risk [Member] Trading Issues Risk [Member] Trading Issues Risk [Member] Value Stocks Investment Risk [Member] Value Stocks Investment 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] Fee Waiver or Reimbursement over Assets, Date of Termination 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] 2014 Annual Return 2014 2015 Annual Return 2015 2016 Annual Return 2016 2017 Annual Return 2017 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 10 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] 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]