Shareholder Report |
12 Months Ended | |||||||||||||||||||||
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Jul. 31, 2026
USD ($)
Holding
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| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Document Type | N-CSR | |||||||||||||||||||||
| Amendment Flag | false | |||||||||||||||||||||
| Registrant Name | First Trust Exchange-Traded Fund III | |||||||||||||||||||||
| Entity Central Index Key | 0001424212 | |||||||||||||||||||||
| Entity Investment Company Type | N-1A | |||||||||||||||||||||
| Document Period End Date | Jul. 31, 2026 | |||||||||||||||||||||
| C000162358 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust Municipal High Income ETF | |||||||||||||||||||||
| Class Name | First Trust Municipal High Income ETF | |||||||||||||||||||||
| Trading Symbol | FMHI | |||||||||||||||||||||
| Security Exchange Name | NASDAQ | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust Municipal High Income ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FMHI. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Material Fund Change Notice [Text Block] |
This report describes changes to the Fund that occurred during or after the reporting period.
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| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/FMHI | |||||||||||||||||||||
| Expenses [Text Block] |
WHAT WERE THE FUND COSTS FOR THE LAST YEAR?
(Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 60 | |||||||||||||||||||||
| Expense Ratio, Percent | 0.58% | |||||||||||||||||||||
| Factors Affecting Performance [Text Block] |
HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE?
The Fund returned 7.59% for the 12-months ended July 31, 2026. The Fund outperformed its blended benchmark, which consists of the following two indexes: 50% of the Bloomberg High Yield 10-Year Municipal Index (8-12 years), and 50% of the Bloomberg Revenue 10-Year Municipal Index (8-12 years). The blended benchmark returned 4.69% for the same Period.
The following key factors impacted the Fund’s performance relative to the blended benchmark during the Period:
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] |
FUND PERFORMANCE (November 1, 2017 to July 31, 2026)
The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods.
Investment Performance of $10,000
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | Nov. 01, 2017 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Material Change Date | Feb. 01, 2026 | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] |
Visit www.ftportfolios.com/etf/FMHI for more recent performance information.
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| Net Assets | $ 994,107,054 | |||||||||||||||||||||
| Holdings Count | Holding | 732 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 5,079,873 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 18.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] |
KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] |
WHAT DID THE FUND INVEST IN? (As of July 31, 2026)
The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund.
Sector Allocation
Credit Quality (1)
(1) The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
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| Credit Quality Explanation [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change. | |||||||||||||||||||||
| Credit Ratings Selection [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. | |||||||||||||||||||||
| Material Fund Change [Text Block] |
HOW HAS THE FUND MATERIALLY CHANGED?
This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FMHI or upon request at 1-800-621-1675 or info@ftportfolios.com.
Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.70% to 0.49% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Material Fund Change Expenses [Text Block] |
Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.70% to 0.49% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Summary of Change Legend [Text Block] |
This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FMHI or upon request at 1-800-621-1675 or info@ftportfolios.com.
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| Updated Prospectus Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Updated Prospectus Email Address | info@ftportfolios.com | |||||||||||||||||||||
| Updated Prospectus Web Address | www.ftportfolios.com/fund-documents/etf/FMHI | |||||||||||||||||||||
| C000172840 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust Horizon Managed Volatility Developed International ETF | |||||||||||||||||||||
| Class Name | First Trust Horizon Managed Volatility Developed International ETF | |||||||||||||||||||||
| Trading Symbol | HDMV | |||||||||||||||||||||
| Security Exchange Name | NYSEArca | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust Horizon Managed Volatility Developed International ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/HDMV. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during or after the reporting period.
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| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/HDMV | |||||||||||||||||||||
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 88 | |||||||||||||||||||||
| Expense Ratio, Percent | 0.81% | [1] | ||||||||||||||||||||
| Extraordinary Expenses Footnote [Text Block] | Includes extraordinary expenses. If these extraordinary expenses were not included, the expense ratio would have been 0.80%. | |||||||||||||||||||||
| Expenses Excluding Extraordinary Expenses, Percent | 0.80% | |||||||||||||||||||||
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE? The Fund returned 17.94% for the 12 months ended July 31, 2026. The Fund underperformed its benchmark, the MSCI EAFE Index, which returned 24.33% for the same Period. The underperformance over the Period was primarily driven by the defensive objective of the strategy capturing less of the return of the benchmark in a period of large gains for the benchmark. Selection of lower volatility securities detracted the most in Japan and Singapore. Selection of lower volatility securities contributed the most in Hong Kong and Sweden. Given the market environment, the Fund performed in-line with expectations, realizing lower drawdowns and lower volatility than the benchmark over the Period.
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] | FUND PERFORMANCE (August 24, 2016 to July 31, 2026) The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods. Investment Performance of $10,000 |
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | Aug. 24, 2016 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] | Visit www.ftportfolios.com/etf/HDMV for more recent performance information.
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| Net Assets | $ 17,488,277 | |||||||||||||||||||||
| Holdings Count | Holding | 151 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 156,752 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 57.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] | WHAT DID THE FUND INVEST IN? (As of July 31, 2026) The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund. Top Ten Holdings
Sector Allocation |
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| Largest Holdings [Text Block] | Top Ten Holdings
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| Material Fund Change [Text Block] | HOW HAS THE FUND MATERIALLY CHANGED? This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/HDMV or upon request at 1-800-621-1675 or info@ftportfolios.com. On September 8, 2026, the Board of Trustees of the Trust (the “Board”) voted to terminate and liquidate HDMV pursuant to a Plan of Liquidation and Termination. The Board determined that the termination and liquidation of HDMV was in the best interests of HDMV. The Fund will liquidate on or around January 15, 2027.
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| Summary of Change Legend [Text Block] | This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/HDMV or upon request at 1-800-621-1675 or info@ftportfolios.com.
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| Updated Prospectus Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Updated Prospectus Email Address | info@ftportfolios.com | |||||||||||||||||||||
| Updated Prospectus Web Address | www.ftportfolios.com/fund-documents/etf/HDMV | |||||||||||||||||||||
| C000172841 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust Horizon Managed Volatility Domestic ETF | |||||||||||||||||||||
| Class Name | First Trust Horizon Managed Volatility Domestic ETF | |||||||||||||||||||||
| Trading Symbol | HUSV | |||||||||||||||||||||
| Security Exchange Name | NYSEArca | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust Horizon Managed Volatility Domestic ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/HUSV. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/HUSV | |||||||||||||||||||||
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 73 | |||||||||||||||||||||
| Expense Ratio, Percent | 0.71% | [2] | ||||||||||||||||||||
| Extraordinary Expenses Footnote [Text Block] | Includes extraordinary expenses. If these extraordinary expenses were not included, the expense ratio would have been 0.70%. | |||||||||||||||||||||
| Expenses Excluding Extraordinary Expenses, Percent | 0.70% | |||||||||||||||||||||
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE? The Fund returned 5.06% for the 12 months ended July 31, 2026. The Fund underperformed its benchmark, the S&P 500® Index, which returned 19.56% for the same Period. The underperformance over the Period was primarily driven by the defensive objective of the strategy capturing less of the return of the benchmark in a period of large gains for the benchmark. Underweights to more volatile sectors like Information Technology and Communication Services detracted from benchmark relative performance, while overweights to the Utilities and Real Estate sectors had a positive excess contribution to return. Additionally, over the Period, a concentrated subset of Information Technology stocks within the benchmark primarily drove returns. The Fund’s systematic strategy avoided holding these companies due to their higher volatility and the inherent risks associated with them. This resulted in underweight allocations to some of the industries experiencing the most gains such as the Semiconductors & Semiconductor Equipment. Given the market environment, the Fund performed in-line with expectations, realizing lower drawdowns and lower volatility than the benchmark over the period.
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] | FUND PERFORMANCE (August 24, 2016 to July 31, 2026) The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods. Investment Performance of $10,000 |
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | Aug. 24, 2016 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] | Visit www.ftportfolios.com/etf/HUSV for more recent performance information.
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| Net Assets | $ 84,086,007 | |||||||||||||||||||||
| Holdings Count | Holding | 102 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 583,835 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 56.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] | WHAT DID THE FUND INVEST IN? (As of July 31, 2026) The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund. Top Ten Holdings
Sector Allocation |
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| Largest Holdings [Text Block] | Top Ten Holdings
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| C000187865 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust California Municipal High Income ETF | |||||||||||||||||||||
| Class Name | First Trust California Municipal High Income ETF | |||||||||||||||||||||
| Trading Symbol | FCAL | |||||||||||||||||||||
| Security Exchange Name | NASDAQ | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust California Municipal High Income ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FCAL. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during or after the reporting period.
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| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/FCAL | |||||||||||||||||||||
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 58 | |||||||||||||||||||||
| Expense Ratio, Percent | 0.56% | |||||||||||||||||||||
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE?
The Fund returned 5.57% for the 12 months ended July 31, 2026. The Fund outperformed its benchmark, the Bloomberg 10 Year California Exempt Index, which returned 3.62% for the same Period. The following key Fund factors impacted the Fund’s performance relative to the benchmark during the Period:
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] | FUND PERFORMANCE (June 20, 2017 to July 31, 2026) The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods. Investment Performance of $10,000 |
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | Jun. 20, 2017 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Material Change Date | Feb. 01, 2026 | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] | Visit www.ftportfolios.com/etf/FCAL for more recent performance information.
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| Net Assets | $ 218,691,665 | |||||||||||||||||||||
| Holdings Count | Holding | 278 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 1,130,105 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 28.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] | WHAT DID THE FUND INVEST IN? (As of July 31, 2026) The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund. Sector Allocation
Credit Quality (1) (1) The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
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| Credit Quality Explanation [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change. | |||||||||||||||||||||
| Credit Ratings Selection [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. | |||||||||||||||||||||
| Material Fund Change [Text Block] | HOW HAS THE FUND MATERIALLY CHANGED? This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FCAL or upon request at 1-800-621-1675 or info@ftportfolios.com. Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.65% to 0.49% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Material Fund Change Expenses [Text Block] | Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.65% to 0.49% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Summary of Change Legend [Text Block] | This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FCAL or upon request at 1-800-621-1675 or info@ftportfolios.com.
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| Updated Prospectus Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Updated Prospectus Email Address | info@ftportfolios.com | |||||||||||||||||||||
| Updated Prospectus Web Address | www.ftportfolios.com/fund-documents/etf/FCAL | |||||||||||||||||||||
| C000205579 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust Ultra Short Duration Municipal ETF | |||||||||||||||||||||
| Class Name | First Trust Ultra Short Duration Municipal ETF | |||||||||||||||||||||
| Trading Symbol | FUMB | |||||||||||||||||||||
| Security Exchange Name | NYSEArca | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust Ultra Short Duration Municipal ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FUMB. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during or after the reporting period.
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| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/FUMB | |||||||||||||||||||||
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 36 | |||||||||||||||||||||
| Expense Ratio, Percent | 0.36% | |||||||||||||||||||||
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE?
The Fund returned 2.37% for the 12 months ended July 31, 2026. The Fund underperformed its benchmark, the Bloomberg Municipal Short-Term Index, which returned 2.67% for the same Period. The following key factors impacted the Fund’s performance relative to its benchmark during the Period:
FUMB did not employ derivatives during the Period. |
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] | FUND PERFORMANCE (November 1, 2018 to July 31, 2026) The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods. Investment Performance of $10,000 |
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | Nov. 01, 2018 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Material Change Date | Feb. 01, 2026 | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] | Visit www.ftportfolios.com/etf/FUMB for more recent performance information.
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| Net Assets | $ 246,416,028 | |||||||||||||||||||||
| Holdings Count | Holding | 249 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 816,106 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 124.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] | WHAT DID THE FUND INVEST IN? (As of July 31, 2026) The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund. Sector Allocation
Credit Quality (1) (1) The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
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| Credit Quality Explanation [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change. | |||||||||||||||||||||
| Credit Ratings Selection [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. | |||||||||||||||||||||
| Material Fund Change [Text Block] | HOW HAS THE FUND MATERIALLY CHANGED? This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FUMB or upon request at 1-800-621-1675 or info@ftportfolios.com. Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.45% to 0.29% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Material Fund Change Expenses [Text Block] | Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.45% to 0.29% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Summary of Change Legend [Text Block] | This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FUMB or upon request at 1-800-621-1675 or info@ftportfolios.com.
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| Updated Prospectus Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Updated Prospectus Email Address | info@ftportfolios.com | |||||||||||||||||||||
| Updated Prospectus Web Address | www.ftportfolios.com/fund-documents/etf/FUMB | |||||||||||||||||||||
| C000205581 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust Short Duration Managed Municipal ETF | |||||||||||||||||||||
| Class Name | First Trust Short Duration Managed Municipal ETF | |||||||||||||||||||||
| Trading Symbol | FSMB | |||||||||||||||||||||
| Security Exchange Name | NYSEArca | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust Short Duration Managed Municipal ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FSMB. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during or after the reporting period.
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| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/FSMB | |||||||||||||||||||||
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 44 | |||||||||||||||||||||
| Expense Ratio, Percent | 0.43% | |||||||||||||||||||||
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE?
The Fund returned 2.78% for the 12 months ended July 31, 2026. The Fund outperformed its benchmark, the Bloomberg Municipal Short (1-5) Year Index, which returned 2.16% for the same Period. The following key factors impacted the Fund’s performance relative to the benchmark during the Period:
The Fund’s use of derivatives had a minimal impact on the Fund’s performance of approximately 1 basis point. |
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] | FUND PERFORMANCE (November 1, 2018 to July 31, 2026) The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods. Investment Performance of $10,000 |
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | Nov. 01, 2018 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Material Change Date | Feb. 01, 2026 | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] | Visit www.ftportfolios.com/etf/FSMB for more recent performance information.
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| Net Assets | $ 621,604,971 | |||||||||||||||||||||
| Holdings Count | Holding | 553 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 2,280,029 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 30.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] | WHAT DID THE FUND INVEST IN? (As of July 31, 2026) The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund. Sector Allocation
Credit Quality (1) (1) The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
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| Credit Quality Explanation [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change. | |||||||||||||||||||||
| Credit Ratings Selection [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. | |||||||||||||||||||||
| Material Fund Change [Text Block] | HOW HAS THE FUND MATERIALLY CHANGED? This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FSMB or upon request at 1-800-621-1675 or info@ftportfolios.com. Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.55% to 0.34% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Material Fund Change Expenses [Text Block] | Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.55% to 0.34% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Summary of Change Legend [Text Block] | This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FSMB or upon request at 1-800-621-1675 or info@ftportfolios.com.
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| Updated Prospectus Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Updated Prospectus Email Address | info@ftportfolios.com | |||||||||||||||||||||
| Updated Prospectus Web Address | www.ftportfolios.com/fund-documents/etf/FSMB | |||||||||||||||||||||
| C000216993 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust Equity Market Neutral ETF | |||||||||||||||||||||
| Class Name | First Trust Equity Market Neutral ETF | |||||||||||||||||||||
| Trading Symbol | NTRL | |||||||||||||||||||||
| Security Exchange Name | NYSEArca | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust Equity Market Neutral ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/NTRL. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during or after the reporting period.
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| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/NTRL | |||||||||||||||||||||
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 136 | [3],[4] | ||||||||||||||||||||
| Expense Ratio, Percent | 1.31% | [3],[4] | ||||||||||||||||||||
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE?
The Fund returned 7.90% for the 12 months ended July 31, 2026 (the “Fiscal Period”). The Fund outperformed its benchmark, the ICE BofA 3-Month U.S. Treasury Bill Index, which returned 3.82% for the same Fiscal Period. As of the close of business on June 23, 2026, the Fund’s name changed from the First Trust Merger Arbitrage ETF to the First Trust Equity Market Neutral ETF and changed its investment strategies and portfolio management team. The First Trust Alternatives Team of First Trust Advisors L.P., the investment advisor to the Fund, assumed portfolio management responsibilities for the Fund, replacing the previous sub-advisor. The Fund no longer pursues a merger arbitrage strategy, instead it seeks an equity market neutral approach where the overall performance of the Fund is driven primarily by the net performance of long and short positions, independent of directional movements in the market. From the close of business on June 23, 2026, through July 31, 2026 (the “Post-Change Period”), the Fund returned 3.50%. During the same Post-Change Period, the Fund’s benchmark returned 0.40%, resulting in Fund outperformance of 3.10 percentage points.
The Fund’s outperformance during the Post-Change Period was primarily attributable to the Fund’s long equity positions outperforming its short equity positions, as well as incremental return from its cash portfolio.
The overall economic backdrop during the Fiscal Period from August 1, 2025, through July 31, 2026, was one of economic growth and strong corporate earnings. During the Fiscal Period, broad-based economic indicators highlighting these trends included:
U.S. equities had strong returns during the Fiscal Period, with two pullbacks (the first in November 2025 and the second in March 2026) unable to derail a solid overall 12 months. For the Fiscal Period, the S&P 500® Index gained 19.56% and the technology-heavy Nasdaq 100®-Index was up 22.58%. Smaller-capitalization stocks performed even better than the larger indexes, posting a return of 34.18% as measured by the Russell 2000® Index. The growth in corporate earnings noted earlier played a large part in boosting equity returns, as did a resilient belief that artificial intelligence will enhance productivity. The Fund’s new investment strategy, implemented as of the close of business on June 23, 2026, benefitted from the generally positive economic backdrop for U.S. equities, as the S&P 500® Index rose by 1.77% during the Post-Change Period. The Fund’s long stock portfolio was up 4.24% on a total return, fully invested basis, while the short stock positions were up 2.84% on the same basis. The short positions detracted from the Fund’s total return because the Fund was short those positions, which rose in value. The positive spread of 1.40% between the two portfolios contributed to the Fund’s overall total return.
During the Post-Change Period, the Fund’s economic exposure to its long positions was targeted at 195% of total Fund assets, while its economic exposure to the short positions was targeted at 175% of total Fund assets. The additional economic exposure above 100% added 4.02% to the Fund’s total return from its long portfolio and detracted -2.13% from total return from its short portfolio. Overall, including the impact of the additional exposure above 100%, the spread between the long and short portfolios was 3.08%. The Fund also benefited from interest income and trade timing, while financing charges related to the total return swaps detracted from performance.
As of July 31, 2026, the Fund had 232 long positions and 251 short positions. Gross equity exposure for the Fund was 356% of the Fund’s net asset value with 192% being long stock positions and 168% in short stock positions. |
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] | FUND PERFORMANCE (February 4, 2020 to July 31, 2026) The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods. Investment Performance of $10,000 |
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | Feb. 04, 2020 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Material Change Date | Jun. 24, 2026 | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] | Visit www.ftportfolios.com/etf/NTRL for more recent performance information.
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| Net Assets | $ 16,257,576 | |||||||||||||||||||||
| Holdings Count | Holding | 17 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 384,617 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 377.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] | WHAT DID THE FUND INVEST IN? (As of July 31, 2026) The table below shows the investment makeup of the Fund, representing the percentage of net assets of the Fund. Fund Allocation
Any amount shown as 0.0% represents less than 0.1%. (1) Includes unrealized appreciation (depreciation) on swap contracts.
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| Material Fund Change [Text Block] | HOW HAS THE FUND MATERIALLY CHANGED? This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/NTRL or upon request at 1-800-621-1675 or info@ftportfolios.com. In its prospectus dated June 22, 2026 and effective June 24, 2026, the Fund’s name changed from “First Trust Merger Arbitrage ETF” to “First Trust Equity Market Neutral ETF,” and the Fund’s ticker changed from “MARB” to “NTRL.” In connection with the change to the Fund’s name, the Fund’s principal investment strategies and principal risks were revised to reflect the Fund’s new strategy to seek an equity market neutral approach where the overall performance of the Fund is driven primarily by the net performance of long and short positions, independent of directional movements in the market. Additionally, the Fund’s annual unitary management fee was reduced to 0.95% of the Fund’s average daily net assets, the Fund’s portfolio management team changed to members of the First Trust Alternatives Investment Team, and the Fund no longer has a sub-advisor.
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| Material Fund Change Name [Text Block] | In its prospectus dated June 22, 2026 and effective June 24, 2026, the Fund’s name changed from “First Trust Merger Arbitrage ETF” to “First Trust Equity Market Neutral ETF,” and the Fund’s ticker changed from “MARB” to “NTRL.” | |||||||||||||||||||||
| Material Fund Change Expenses [Text Block] | Additionally, the Fund’s annual unitary management fee was reduced to 0.95% of the Fund’s average daily net assets, the Fund’s portfolio management team changed to members of the First Trust Alternatives Investment Team, and the Fund no longer has a sub-advisor. | |||||||||||||||||||||
| Material Fund Change Strategies [Text Block] | In connection with the change to the Fund’s name, the Fund’s principal investment strategies and principal risks were revised to reflect the Fund’s new strategy to seek an equity market neutral approach where the overall performance of the Fund is driven primarily by the net performance of long and short positions, independent of directional movements in the market. | |||||||||||||||||||||
| Material Fund Change Risks Change [Text Block] | In connection with the change to the Fund’s name, the Fund’s principal investment strategies and principal risks were revised to reflect the Fund’s new strategy to seek an equity market neutral approach where the overall performance of the Fund is driven primarily by the net performance of long and short positions, independent of directional movements in the market. | |||||||||||||||||||||
| Summary of Change Legend [Text Block] | This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/NTRL or upon request at 1-800-621-1675 or info@ftportfolios.com.
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| Updated Prospectus Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Updated Prospectus Email Address | info@ftportfolios.com | |||||||||||||||||||||
| Updated Prospectus Web Address | www.ftportfolios.com/fund-documents/etf/NTRL | |||||||||||||||||||||
| C000218390 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust Horizon Managed Volatility Small/Mid ETF | |||||||||||||||||||||
| Class Name | First Trust Horizon Managed Volatility Small/Mid ETF | |||||||||||||||||||||
| Trading Symbol | HSMV | |||||||||||||||||||||
| Security Exchange Name | NYSEArca | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust Horizon Managed Volatility Small/Mid ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/HSMV. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during or after the reporting period.
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| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/HSMV | |||||||||||||||||||||
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 86 | |||||||||||||||||||||
| Expense Ratio, Percent | 0.81% | [5] | ||||||||||||||||||||
| Extraordinary Expenses Footnote [Text Block] | Includes extraordinary expenses. If these extraordinary expenses were not included, the expense ratio would have been 0.80%. | |||||||||||||||||||||
| Expenses Excluding Extraordinary Expenses, Percent | 0.80% | |||||||||||||||||||||
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE? The Fund returned 12.80% for the 12 months ended July 31, 2026. The Fund underperformed its benchmark, the S&P 1000® Index, which returned 24.91% for the same Period. The underperformance over the Period was primarily driven by the defensive objective of the strategy capturing less of the return of the benchmark in a period of large gains for the benchmark. Small and mid-sized stocks in the benchmark generally led larger cap stocks over the same Period, as these companies have exhibited characteristics more sensitive to an improving macro-economic environment. Underweights to more volatile sectors such as Information Technology and Health Care were large benchmark relative detractors, while overweights to Utilities and Real Estate were accretive. Given the market environment, the Fund performed in-line with expectations, realizing lower drawdowns and lower volatility than the benchmark over the Period.
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] | FUND PERFORMANCE (April 6, 2020 to July 31, 2026) The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods. Investment Performance of $10,000 |
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | Apr. 06, 2020 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] | Visit www.ftportfolios.com/etf/HSMV for more recent performance information.
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| Net Assets | $ 35,208,002 | |||||||||||||||||||||
| Holdings Count | Holding | 151 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 235,393 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 40.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] | WHAT DID THE FUND INVEST IN? (As of July 31, 2026) The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund. Top Ten Holdings
Sector Allocation |
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| Largest Holdings [Text Block] | Top Ten Holdings
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| Material Fund Change [Text Block] | HOW HAS THE FUND MATERIALLY CHANGED? This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/HSMV or upon request at 1-800-621-1675 or info@ftportfolios.com. On September 8, 2026, the Board of Trustees of the Trust (the “Board”) voted to terminate and liquidate HSMV pursuant to a Plan of Liquidation and Termination. The Board determined that the termination and liquidation of HSMV was in the best interests of HSMV. The Fund will liquidate on or around January 15, 2027.
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| Summary of Change Legend [Text Block] | This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/HSMV or upon request at 1-800-621-1675 or info@ftportfolios.com.
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| Updated Prospectus Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Updated Prospectus Email Address | info@ftportfolios.com | |||||||||||||||||||||
| Updated Prospectus Web Address | www.ftportfolios.com/fund-documents/etf/HSMV | |||||||||||||||||||||
| C000223991 [Member] | ||||||||||||||||||||||
| Shareholder Report [Line Items] | ||||||||||||||||||||||
| Fund Name | First Trust New York Municipal High Income ETF | |||||||||||||||||||||
| Class Name | First Trust New York Municipal High Income ETF | |||||||||||||||||||||
| Trading Symbol | FMNY | |||||||||||||||||||||
| Security Exchange Name | NYSEArca | |||||||||||||||||||||
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the First Trust New York Municipal High Income ETF (the “Fund”) for the year of August 1, 2025 to July 31, 2026 (the “Period”). | |||||||||||||||||||||
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |||||||||||||||||||||
| Additional Information [Text Block] | You can find additional information about the Fund at www.ftportfolios.com/fund-documents/etf/FMNY. You can also request this information by contacting us at 1-800-621-1675 or info@ftportfolios.com. | |||||||||||||||||||||
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during or after the reporting period.
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| Additional Information Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Additional Information Email | info@ftportfolios.com | |||||||||||||||||||||
| Additional Information Website | www.ftportfolios.com/fund-documents/etf/FMNY | |||||||||||||||||||||
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (Based on a hypothetical $10,000 investment)
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| Expenses Paid, Amount | $ 57 | |||||||||||||||||||||
| Expense Ratio, Percent | 0.55% | |||||||||||||||||||||
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR? WHAT AFFECTED THE FUND’S PERFORMANCE?
The Fund returned 5.85% for the 12 months ended July 31, 2026. The Fund underperformed its benchmark, the Bloomberg Municipal New York 12-17 Years Index, which returned 6.43% for the same Period. The following key Fund factors impacted Fund performance relative to the benchmark during the Period:
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| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. | |||||||||||||||||||||
| Line Graph [Table Text Block] | FUND PERFORMANCE (May 12, 2021 to July 31, 2026) The performance line graph below shows the performance of a hypothetical $10,000 initial investment in the Fund over a ten-year period (or for the life of the Fund, if shorter). The subsequent account value as of the end of the Period is listed next to the name of the Fund or index, as applicable. The performance table below shows the average annual total returns of the Fund for the past one-, five-, and ten-year periods, as applicable (or for the life of the Fund, if shorter), as of the end of the Period. Both the line graph and performance table compare the Fund’s performance to an appropriate broad-based index and may compare to additional indices reflecting the market segment(s) in which the Fund invests over the same periods. Investment Performance of $10,000 |
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| Average Annual Return [Table Text Block] |
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| Performance Inception Date | May 12, 2021 | |||||||||||||||||||||
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |||||||||||||||||||||
| Material Change Date | Feb. 01, 2026 | |||||||||||||||||||||
| Updated Performance Information Location [Text Block] | Visit www.ftportfolios.com/etf/FMNY for more recent performance information.
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| Net Assets | $ 38,088,329 | |||||||||||||||||||||
| Holdings Count | Holding | 110 | |||||||||||||||||||||
| Advisory Fees Paid, Amount | $ 163,705 | |||||||||||||||||||||
| Investment Company Portfolio Turnover | 24.00% | |||||||||||||||||||||
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (As of July 31, 2026)
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| Holdings [Text Block] | WHAT DID THE FUND INVEST IN? (As of July 31, 2026) The tables below show the investment makeup of the Fund, representing the percentage of total investments of the Fund. Sector Allocation
Credit Quality (1) (1) The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
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| Credit Quality Explanation [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. For situations in which a security is rated by more than one NRSRO and the ratings are not equivalent, the highest rating is used. Sub-investment grade ratings are those rated BB+/Ba1 or lower. Investment grade ratings are those rated BBB-/Baa3 or higher. “NR” indicates no rating. The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change. | |||||||||||||||||||||
| Credit Ratings Selection [Text Block] | The credit quality and ratings information presented above reflect the ratings assigned by one or more nationally recognized statistical rating organizations (NRSROs), including S&P Global Ratings, Moody’s Investors Service, Inc., Fitch Ratings or a comparably rated NRSRO. | |||||||||||||||||||||
| Material Fund Change [Text Block] | HOW HAS THE FUND MATERIALLY CHANGED? This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FMNY or upon request at 1-800-621-1675 or info@ftportfolios.com. Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.65% to 0.49% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Material Fund Change Expenses [Text Block] | Effective February 1, 2026, the Fund’s annual unitary management fee was reduced from 0.65% to 0.49% of the Fund’s average daily net assets. Additionally, the Fund is no longer eligible for any breakpoint discounts described in the Fund’s prospectus or statement of additional information.
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| Summary of Change Legend [Text Block] | This is a summary of certain changes to the Fund since August 1, 2025. For more complete information, you may review the Fund’s prospectus and any applicable supplements at www.ftportfolios.com/fund-documents/etf/FMNY or upon request at 1-800-621-1675 or info@ftportfolios.com.
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| Updated Prospectus Phone Number | 1-800-621-1675 | |||||||||||||||||||||
| Updated Prospectus Email Address | info@ftportfolios.com | |||||||||||||||||||||
| Updated Prospectus Web Address | www.ftportfolios.com/fund-documents/etf/FMNY | |||||||||||||||||||||
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