First Trust SMID Capital Strength ETF Performance Management - First Trust SMID Capital Strength ETF |
Mar. 31, 2025 |
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| Prospectus [Line Items] | |
| Bar Chart and Performance Table [Heading] | <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Annual Total Return</span> |
| Performance Narrative [Text Block] | The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value as well as the average annual Fund and Index returns. The bar chart and table provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual total returns based on net asset value compared to those of the Index, the Fund's prior index, a broad-based securities market index and a market index. The Fund’s performance information is accessible on the Fund’s website at http://www.ftportfolios.com. On June 7, 2024, the Fund’s underlying index changed from the Nasdaq Riskalyze US Mid CapTM Index to The SMID Capital Strength Index. Therefore, any Fund performance and historical returns shown below that incorporate Fund performance prior to June 7, 2024 reflect performance of the Fund based on the Nasdaq Riskalyze US Mid CapTM Index and are not necessarily indicative of the performance that the Fund, based on The SMID Capital Strength Index, would have generated. |
| Performance Past Does Not Indicate Future [Text] | <span style="color:#000000;font-family:Arial;font-size:9.00pt;">The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.</span> |
| Performance Information Illustrates Variability of Returns [Text] | <span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value as well as the average annual Fund and Index returns. The bar chart and table provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual total returns based on net asset value compared to those of the Index, </span><span style="font-family:Arial;font-size:9.00pt;">the Fund's prior index, a broad-based securities market index and a market index. </span> |
| Bar Chart [Heading] | <span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">First Trust SMID Capital Strength ETF</span> <br/><span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">Calendar Year Total Returns as of 12/31 </span><span style="font-family:Arial;font-size:7pt;font-weight:bold;position:relative;top:-3.25pt;">(1)</span> |
| Bar Chart Footnotes [Text Block] | (1)The Fund's calendar year-to-date total return based on net asset value for the period 12/31/24 to 06/30/25 was 1.26%. |
| Bar Chart Closing [Text Block] | During the periods shown in the chart above:ReturnPeriod EndedBest Quarter24.70%December 31, 2020Worst Quarter-32.34%March 31, 2020Year-to-Date1.26%June 30, 2025 |
| Performance Table Heading | <span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">Average Annual Total Returns for the Periods Ended December 31, 2024</span> |
| Performance Table Market Index Changed | <span style="font-family:Arial;font-size:8.10pt;font-style:italic;">On June 7, 2024, the Fund’s underlying index changed from the Nasdaq Riskalyze US Mid Cap</span><span style="font-family:Arial;font-size:5.5pt;font-style:italic;position:relative;top:-2.75pt;">TM</span><span style="font-family:Arial;font-size:8.10pt;font-style:italic;"> Index to The SMID Capital Strength Index. Therefore, the Fund’s performance and historical returns shown for the periods prior to this</span><span style="font-family:Arial;font-size:8.10pt;font-style:italic;line-height:9.00pt;"> </span><span style="font-family:Arial;font-size:8.10pt;font-style:italic;">date</span><span style="font-family:Arial;font-size:8.10pt;font-style:italic;line-height:9.00pt;"> </span><span style="font-family:Arial;font-size:8.10pt;font-style:italic;">are not necessarily indicative of the performance that the Fund, based on its current index, would have generated.</span> |
| Performance Table Uses Highest Federal Rate | <span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax.</span> |
| Performance Table Not Relevant to Tax Deferred | <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;font-style:italic;">IRAs</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">) or employee-sponsored retirement plans.</span> |
| Performance Table Explanation after Tax Higher | <span style="font-family:Arial;font-size:9.00pt;">Returns after taxes on distributions reflect the taxed return on the payment of dividends </span><span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for </span><span style="font-family:Arial;font-size:9.00pt;">an index do not include expenses, which are deducted from Fund returns, or taxes.</span> |
| Performance Availability Website Address [Text] | <span style="font-family:Arial;font-size:9.00pt;">http://www.ftportfolios.com</span> |
| First Trust SMID Capital Strength ETF | |
| Prospectus [Line Items] | |
| Year to Date Return, Label [Optional Text] | <span style="font-family:Arial;font-size:9.00pt;margin-left:0.0pt;">Year-to-Date</span> |
| Bar Chart, Year to Date Return | 1.26% |
| Bar Chart, Year to Date Return, Date | Jun. 30, 2025 |
| Highest Quarterly Return, Label [Optional Text] | <span style="font-family:Arial;font-size:9.00pt;margin-left:0.0pt;">Best Quarter</span> |
| Highest Quarterly Return | 24.70% |
| Highest Quarterly Return, Date | Dec. 31, 2020 |
| Lowest Quarterly Return, Label [Optional Text] | <span style="font-family:Arial;font-size:9.00pt;margin-left:0.0pt;">Worst Quarter</span> |
| Lowest Quarterly Return | (32.34%) |
| Lowest Quarterly Return, Date | Mar. 31, 2020 |