Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Jan. 04, 2021
First Trust Active Factor Small Cap ETF
Risk Return Abstract	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Summary Information
Objective [Heading]	rr_ObjectiveHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;margin-left:0%;">Investment Objective</span>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The First Trust Active Factor Small Cap ETF (the "Fund") seeks to provide capital appreciation.
Expense [Heading]	rr_ExpenseHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;margin-left:0%;">Fees and Expenses of the Fund</span>
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table describes the fees and expenses you may pay if you buy, hold and sell shares of the Fund. Investors may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	<span style="color:#000000;font-family:Arial;font-size:9.00pt;font-weight:bold;margin-left:0%;">Shareholder Fees</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(fees paid directly from your investment)</span>
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	<span style="color:#000000;font-family:Arial;font-size:9.00pt;font-weight:bold;margin-left:0%;">Annual Fund Operating Expenses</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(expenses that you pay each year as a percentage of the value of your investment)</span>
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;margin-left:0%;">Portfolio Turnover</span>
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the fiscal period December 3, 2019 (inception) through August 31, 2020, the Fund’s portfolio turnover rate was 65% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	65.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	<span style="color:#000000;font-family:Arial;font-size:9.00pt;font-style:italic;font-weight:bold;margin-left:0%;">Example</span>
Expense Example, No Redemption Narrative [Text Block]	rr_ExpenseExampleNoRedemptionNarrativeTextBlock	The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. This example does not take into account customary brokerage commissions that you pay when purchasing or selling shares of the Fund in the secondary market.The example assumes that you invest $10,000 in the Fund for the time periods indicated. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain at current levels. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;margin-left:0%;">Principal Investment Strategies</span>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal market conditions, the Fund will invest at least 80% of its net assets (including investment borrowings) in U.S.-listed equity securities issued by small capitalization companies. The Fund defines small capitalization companies as those that, at the time of investment, have a market capitalization between a minimum of $250 million and the maximum market capitalization of a widely recognized index of small capitalization companies based upon the composition of the index at the time of investment. As of November 30, 2020, the maximum market capitalization of the referenced index was $14.19 billion. The Fund is not required to sell a security if its market capitalization increases above the Fund’s maximum market capitalization at any time after its acquisition by the Fund.The Fund is actively managed primarily relying on a multi-factor quantitative methodology with active risk management to construct a portfolio of securities exhibiting exposures to one or more investing factors. The multi-factor quantitative methodology currently used by the Fund may take into account the following factors: (i) value; (ii) momentum; (iii) quality; and (iv) low volatility. These factors are briefly defined below.•Value is a measure of a security’s price relative to the fundamental value of that security.•Momentum is a measure of the price performance of a security versus a market average, another security or universe of securities.•Quality is a measure of the strength of a security’s fundamentals.•Volatility is a measure of the magnitude of a security’s price fluctuations over time.The Fund’s active strategy gives it the flexibility to alter the investing factors used in the construction of the Fund’s portfolio in response to changes in market conditions, emergent academic research or other considerations. The Fund’s active risk management allows the investment advisor to maintain exposure to desired factors while controlling exposure to industries/sectors, single stock risk and other risks.The Fund is classified as “non-diversified” under the Investment Company Act of 1940, as amended (the “1940 Act”).
Risk [Heading]	rr_RiskHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;margin-left:0%;">Principal Risks</span>
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. There can be no assurance that the Fund’s investment objective will be achieved. The order of the below risk factors does not indicate the significance of any particular risk factor.AUTHORIZED PARTICIPANT CONCENTRATION RISK. Only an authorized participant may engage in creation or redemption transactions directly with the Fund. A limited number of institutions act as authorized participants for the Fund. To the extent that these institutions exit the business or are unable to proceed with creation and/or redemption orders and no other authorized participant steps forward to create or redeem, the Fund’s shares may trade at a premium or discount to the Fund’s net asset value and possibly face delisting.CYBER SECURITY RISK. The Fund is susceptible to operational risks through breaches in cyber security. A breach in cyber security refers to both intentional and unintentional events that may cause the Fund to lose proprietary information, suffer data corruption or lose operational capacity. Such events could cause the Fund to incur regulatory penalties, reputational damage, additional compliance costs associated with corrective measures and/or financial loss. Cyber security breaches may involve unauthorized access to the Fund’s digital information systems through “hacking” or malicious software coding but may also result from outside attacks such as denial-of-service attacks through efforts to make network services unavailable to intended users. In addition, cyber security breaches of the issuers of securities in which the Fund invests or the Fund’s third-party service providers, such as its administrator, transfer agent, custodian, or sub-advisor, as applicable, can also subject the Fund to many of the same risks associated with direct cyber security breaches. Although the Fund has established risk management systems designed to reduce the risks associated with cyber security, there is no guarantee that such efforts will succeed, especially because the Fund does not directly control the cyber security systems of issuers or third-party service providers.EQUITY SECURITIES RISK. The value of the Fund’s shares will fluctuate with changes in the value of the equity securities in which it invests. Equity securities prices fluctuate for several reasons, including changes in investors’ perceptions of the financial condition of an issuer or the general condition of the relevant equity market, such as market volatility, or when political or economic events affecting an issuer occur. Common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase. Equity securities may decline significantly in price over short or extended periods of time, and such declines may occur in the equity market as a whole, or they may occur in only a particular country, company, industry or sector of the market.INDEX CONSTITUENT RISK. The Fund may be a constituent of one or more indices. As a result, the Fund may be included in one or more index-tracking exchange-traded funds or mutual funds. Being a component security of such a vehicle could greatly affect the trading activity involving the Fund’s shares, the size of the Fund and the market volatility of the Fund. Inclusion in an index could increase demand for the Fund and removal from an index could result in outsized selling activity in a relatively short period of time. As a result, the Fund’s net asset value could be negatively impacted and the Fund’s market price may be below the Fund’s net asset value during certain periods. In addition, index rebalances may potentially result in increased trading activity in the Fund’s shares.LOW VOLATILITY RISK. Although subject to the risks of common stocks, low volatility stocks are seen as having a lower risk profile than the overall markets. However, a portfolio comprised of low volatility stocks may not produce investment exposure that has lower variability to changes in such stocks’ price levels. Low volatility stocks are likely to underperform the broader market during periods of rapidly rising stock prices.MANAGEMENT RISK. The Fund is subject to management risk because it is an actively managed portfolio. In managing the Fund’s investment portfolio, the portfolio managers will apply investment techniques and risk analyses that may not produce the desired result. There can be no guarantee that the Fund will meet its investment objective.MARKET CAPITALIZATION DEVIATION RISK. The Fund uses the market capitalization range of a widely recognized index to determine the securities that are within the Fund’s market capitalization range. During periods between the index’s reconstitution dates, the market capitalization of the companies in the index will change due to market movement and other factors, and the market capitalization range of the index may change significantly. Accordingly, the Fund may acquire securities that would fall outside of the market capitalization range of the index or would not meet the index’s eligibility criteria on a reconstitution date. The Fund is also not required to sell a security at any time solely because the market capitalization of the issuer of the security has increased or decreased to a size that would fall outside of the market capitalization range of the index or would not meet the index’s eligibility criteria on a reconstitution date. As a result, the Fund may be exposed to the risks associated with securities of different market capitalizations or investors may not be given the opportunity to invest fully in the Fund’s intended market capitalization range.MARKET MAKER RISK. The Fund faces numerous market trading risks, including the potential lack of an active market for Fund shares due to a limited number of market markers. Decisions by market makers or authorized participants to reduce their role or step away from these activities in times of market stress could inhibit the effectiveness of the arbitrage process in maintaining the relationship between the underlying values of the Fund’s portfolio securities and the Fund’s market price. The Fund may rely on a small number of third-party market makers to provide a market for the purchase and sale of shares. Any trading halt or other problem relating to the trading activity of these market makers could result in a dramatic change in the spread between the Fund’s net asset value and the price at which the Fund’s shares are trading on the Exchange, which could result in a decrease in value of the Fund’s shares. This reduced effectiveness could result in Fund shares trading at a discount to net asset value and also in greater than normal intraday bid-ask spreads for Fund shares.MARKET RISK. Market risk is the risk that a particular security, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by such factors as economic, political, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Shares of the Fund could decline in value or underperform other investments. In addition, local, regional or global events such as war, acts of terrorism, spread of infectious diseases or other public health issues, recessions, or other events could have a significant negative impact on the Fund and its investments. For example, the coronavirus disease 2019 (COVID-19) global pandemic and the aggressive responses taken by many governments, including closing borders, restricting international and domestic travel, and the imposition of prolonged quarantines or similar restrictions, has had negative impacts, and in many cases severe impacts, on markets worldwide. Additionally, the COVID-19 pandemic has caused prolonged disruptions to the normal business operations of companies around the world and the impact of such disruptions is hard to predict. Such events may affect certain geographic regions, countries, sectors and industries more significantly than others. Such events could adversely affect the prices and liquidity of the Fund’s portfolio securities or other instruments and could result in disruptions in the trading markets. Any of such circumstances could have a materially negative impact on the value of the Fund’s shares and result in increased market volatility. During any such events, the Fund’s shares may trade at increased premiums or discounts to their net asset value.MODEL RISK. The Fund’s portfolio managers use quantitative models to help construct the Fund’s portfolio. The utilization of quantitative models entails the risk that a model may be limited or incorrect, that the data on which a model relies may be incorrect or incomplete and that the portfolio managers may not be successful in selecting companies for investment or determining the weighting of particular stocks in the Fund’s portfolio. To the extent that the model is based upon incorrect or incomplete data, the Fund could be induced to buy certain investments at prices that are too high, to sell certain other investments at prices that are too low or to miss favorable opportunities altogether. Any of these factors could cause the Fund to underperform funds with similar strategies that do not rely on quantitative analysis for portfolio construction.MOMENTUM INVESTING RISK. The Fund employs a “momentum” style of investing that emphasizes selecting stocks that have had higher recent price performance compared to other stocks. Momentum can change quickly and stocks that previously exhibited high momentum characteristics may not experience positive momentum or may experience more volatility than the market as a whole. In addition, there may be periods when the momentum style of investing is out of favor and the investment performance of the Fund may suffer.NON-DIVERSIFICATION RISK. The Fund is classified as “non-diversified” under the 1940 Act. As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended. The Fund may invest a relatively high percentage of its assets in a limited number of issuers. As a result, the Fund may be more susceptible to a single adverse economic or regulatory occurrence affecting one or more of these issuers, experience increased volatility and be highly invested in certain issuers.PREMIUM/DISCOUNT RISK. The market price of the Fund’s shares will generally fluctuate in accordance with changes in the Fund’s net asset value as well as the relative supply of and demand for shares on the Exchange. The Fund’s investment advisor cannot predict whether shares will trade below, at or above their net asset value because the shares trade on the Exchange at market prices and not at net asset value. Price differences may be due, in large part, to the fact that supply and demand forces at work in the secondary trading market for shares will be closely related, but not identical, to the same forces influencing the prices of the holdings of the Fund trading individually or in the aggregate at any point in time. However, given that shares can only be purchased and redeemed in Creation Units, and only to and from broker-dealers and large institutional investors that have entered into participation agreements (unlike shares of closed-end funds, which frequently trade at appreciable discounts from, and sometimes at premiums to, their net asset value), the Fund’s investment advisor believes that large discounts or premiums to the net asset value of shares should not be sustained. During stressed market conditions, the market for the Fund’s shares may become less liquid in response to deteriorating liquidity in the market for the Fund’s underlying portfolio holdings, which could in turn lead to differences between the market price of the Fund’s shares and their net asset value.QUALITY STOCKS INVESTMENT RISK. A quality style of investing emphasizes companies with strong fundamentals. However, there is no guarantee that the Fund will correctly identify companies with strong fundamentals or that selected companies will maintain strong fundamentals. In addition, quality stocks are subject to the risk that the returns on quality securities are less than returns on other styles of investing or the overall stock market.SIGNIFICANT EXPOSURE RISK. To the extent that the Fund invests a large percentage of its assets in a single asset class or industry or sector, an adverse economic, business or political development may affect the value of the Fund’s investments more than if the Fund were more broadly diversified. A significant exposure makes the Fund more susceptible to any single occurrence and may subject the Fund to greater market risk than a fund that is more broadly diversified.SMALL CAPITALIZATION COMPANIES RISK. Small capitalization companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than large and mid capitalization companies as a result of several factors, including limited trading volumes, fewer products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than large and mid capitalization companies.TRADING ISSUES RISK. Trading in Fund shares on the Exchange may be halted due to market conditions or for reasons that, in the view of the Exchange, make trading in shares inadvisable. In addition, trading in Fund shares on the Exchange is subject to trading halts caused by extraordinary market volatility pursuant to the Exchange’s “circuit breaker” rules. There can be no assurance that the requirements of the Exchange necessary to maintain the listing of the Fund will continue to be met or will remain unchanged. The Fund may have difficulty maintaining its listing on the Exchange in the event the Fund’s assets are small, the Fund does not have enough shareholders, or if the Fund is unable to proceed with creation and/or redemption orders.VALUE STOCKS INVESTMENT RISK. The intrinsic value of a stock with value characteristics may not be fully recognized by the market for a long time or a stock judged to be undervalued may actually be appropriately priced at a low level.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;margin-left:0%;">Performance</span>
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The Fund has not yet operated for a full calendar year and, therefore, performance information is not included in this section of the prospectus. See "Total Return Information" for performance information regarding the Fund.
First Trust Active Factor Small Cap ETF | First Trust Active Factor Small Cap ETF
Risk Return Abstract	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	none
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.02%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.77%
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 79
3 Years	rr_ExpenseExampleNoRedemptionYear03	246
5 Years	rr_ExpenseExampleNoRedemptionYear05	428
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 954