Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	First Trust Exchange-Traded Fund II
Prospectus Date	rr_ProspectusDate	Feb. 01, 2023
First Trust Indxx Global Natural Resources Income 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;">Investment Objective</span>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The First Trust Indxx Global Natural Resources Income ETF (the “Fund”) seeks investment results that correspond generally to the price and yield (before the Fund’s fees and expenses) of an equity index called the Indxx Global Natural Resources Income Index (the “Index”).
Expense [Heading]	rr_ExpenseHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">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;">Shareholder Fees</span> <br/><span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">(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;">Annual Fund Operating Expenses</span> <br/><span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">(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;">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 most recent fiscal year, the Fund’s portfolio turnover rate was 69% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	69.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	<span style="color:#000000;font-family:Arial;font-size:9.00pt;font-style:italic;font-weight:bold;">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.The example assumes that you invest $10,000 in the Fund for the time periods indicated and then hold or sell all of your shares at the end of those periods. 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;">Principal Investment Strategies</span>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund will normally invest at least 90% of its net assets (including investment borrowings) in the common stocks and depositary receipts that comprise the Index. The Fund, using an indexing investment approach, attempts to replicate, before fees and expenses, the performance of the Index. The Index is owned, developed, maintained and sponsored by Indxx, Inc.(the “Index Provider”). The Index Provider reserves the right to use qualitative judgment to include, exclude, adjust, or postpone the inclusion of a stock in the Index. Continued Index membership of a constituent is not necessarily subject to the guidelines provided in the Index methodology. A security may be considered for exclusion by the Index Provider on the basis of corporate governance, accounting policies, lack of transparency and lack of representation, despite meeting all the criteria provided in the Index methodology.According to the Index Provider, the Index is a free float adjusted market capitalization weighted index designed to measure the market performance of the 50 highest dividend yielding companies involved in the upstream (i.e., generally exploration and production) segment of the natural resources sector. The term “free float” describes the portion of an issuer’s outstanding securities that can be publicly traded, and therefore excludes locked-in securities held by an issuer’s affiliates, officers or promoters or securities subject to some other restrictive arrangement that prevents them from being freely traded. Component securities may represent the following businesses: oil and gas exploration and production; integrated oil and gas companies; coal; steel; gold; aluminum; diversified metal and mining; industrial metals; precious metals; water; agricultural products; beverages; agricultural chemicals and fertilizers; and paper and forest products. The Index Provider’s classification of an issuer and its business may be different than any other standardized industry classification applied to the issuer and may reflect only a portion of the issuer’s business activities. Consequently, because an issuer’s principal business activity may be outside the natural resources sector, the Fund’s portfolio may include significant holdings of issuers that the Index Provider classifies in a sector that would otherwise not typically fall within the focus of the Index if classified by a different standard.According to the Index Provider, to be included in the Index, a security must be issued by a company that has (i) a positive earnings-per-share for the preceding 12 months, (ii) paid dividends in each of the prior two years and (iii) paid dividends over the preceding 12 months greater than or equal to the dividends it paid over the same 12-month period one year prior. In addition, a security must meet certain additional criteria, including that it must have a minimum free float equivalent to 10% of shares outstanding, a minimum market capitalization of $1 billion and meet certain liquidity-related requirements that focus on trading activity. Companies may generally be domiciled in any country, including emerging market countries, subject to certain exclusions determined by the Index Provider. Each eligible security is classified into five broad categories: energy, materials, agriculture, water and timber. The 50 securities with the highest dividend yield are included in the Index. The Index is then adjusted to ensure that no more than 30% of the Index's components are classified as comprising one of the five categories. Under normal market conditions, the Fund invests at least 40% of its net assets (including investment borrowings) in securities of non-U.S. issuers and invests in the securities of issuers located in at least three countries. The Fund may also invest in U.S. dollar denominated and non-U.S. dollar denominated securities.The Index is reconstituted annually and rebalanced quarterly and the Fund will make corresponding changes to its portfolio shortly after the Index changes are made public. The Index’s quarterly rebalance schedule may cause the Fund to experience a higher rate of portfolio turnover. The Fund will be concentrated in an industry or a group of industries to the extent that the Index is so concentrated. As of December 31, 2022, the Fund had significant investments in materials companies and energy companies, although this may change from time to time. To the extent the Fund invests a significant portion of its assets in a given jurisdiction or investment sector, the Fund may be exposed to the risks associated with that jurisdiction or investment sector.
Risk [Heading]	rr_RiskHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">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.AGRICULTURE COMPANIES RISK. Economic forces, including forces affecting agricultural markets, as well as government policies and regulations affecting agriculture companies, could adversely impact the Fund's investments. Agricultural and livestock production and trade flows are significantly affected by government policies and regulations. Governmental policies affecting agriculture companies, such as taxes, tariffs, duties, subsidies and import and export restrictions on agricultural commodities, commodity products and livestock, can influence agriculture company profitability, the planting/raising of certain crops/livestock versus other uses of resources, the location and size of crop and livestock production, whether unprocessed or processed commodity products are traded and the volume and types of imports and exports. In addition, companies in the agriculture sector must comply with a broad range of environmental laws and regulations.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 (the difference between the market price of the Fund's shares and the Fund's net asset value) and possibly face delisting and the bid/ask spread (the difference between the price that someone is willing to pay for shares of the Fund at a specific point in time versus the price at which someone is willing to sell) on the Fund’s shares may widen.CURRENCY RISK. Changes in currency exchange rates affect the value of investments denominated in a foreign currency, and therefore the value of such investments in the Fund’s portfolio. The Fund’s net asset value could decline if a currency to which the Fund has exposure depreciates against the U.S. dollar or if there are delays or limits on repatriation of such currency. Currency exchange rates can be very volatile and can change quickly and unpredictably. As a result, the value of an investment in the Fund may change quickly and without warning.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.DEPOSITARY RECEIPTS RISK. Depositary receipts represent equity interests in a foreign company that trade on a local stock exchange. Depositary receipts may be less liquid than the underlying shares in their primary trading market. Any distributions paid to the holders of depositary receipts are usually subject to a fee charged by the depositary. Holders of depositary receipts may have limited voting rights, and investment restrictions in certain countries may adversely impact the value of depositary receipts because such restrictions may limit the ability to convert the equity shares into depositary receipts and vice versa. Such restrictions may cause the equity shares of the underlying issuer to trade at a discount or premium to the market price of the depositary receipts.DIVIDENDS RISK. The Fund’s investment in dividend-paying securities could cause the Fund to underperform similar funds that invest without consideration of an issuer’s track record of paying dividends. Companies that issue dividend-paying securities are not required to continue to pay dividends on such securities. Therefore, there is the possibility that such companies could reduce or eliminate the payment of dividends in the future, which could negatively affect the Fund’s performance.EMERGING MARKETS RISK. Investments in securities issued by governments and companies operating in emerging market countries involve additional risks relating to political, economic, or regulatory conditions not associated with investments in securities and instruments issued by U.S. companies or by companies operating in other developed market countries. Investments in emerging markets securities are generally considered speculative in nature and are subject to the following heightened risks: smaller market capitalization of securities markets which may suffer periods of relative illiquidity; significant price volatility; restrictions on foreign investment; possible repatriation of investment income and capital; rapid inflation; and currency convertibility issues. Emerging market countries also often have less uniformity in accounting, auditing and reporting requirements, unsettled securities laws, unreliable securities valuation and greater risk associated with custody of securities. Financial and other reporting by companies and government entities also may be less reliable in emerging market countries. Shareholder claims that are available in the U.S., as well as regulatory oversight and authority that is common in the U.S., including for claims based on fraud, may be difficult or impossible for shareholders of securities in emerging market countries or for U.S. authorities to pursue. The index the Fund seeks to track may not weight the securities in emerging market countries on the basis of investor protection limitations, financial reporting quality or available oversight mechanisms. Furthermore, investors may be required to register the proceeds of sales and future economic or political crises could lead to price controls, forced mergers, expropriation or confiscatory taxation, seizure, nationalization or creation of government monopolies.ENERGY COMPANIES RISK. The success of energy companies may be cyclical and highly dependent on energy prices. The market value of securities issued by energy companies may decline for many reasons, including, among other things, changes in the levels and volatility of global energy prices, energy supply and demand, capital expenditures on exploration and production of energy sources, exchange rates, interest rates, economic conditions, tax treatment, energy conservation efforts, increased competition and technological advances. Energy companies may be subject to substantial government regulation and contractual fixed pricing, which may increase the cost of doing business and limit the earnings of these companies. A significant portion of the revenues of energy companies may depend on a relatively small number of customers, including governmental entities and utilities. As a result, governmental budget constraints may have a material adverse effect on the stock prices of energy companies. Energy companies may also operate in, or engage in transactions involving, countries with less developed regulatory regimes or a history of expropriation, nationalization or other adverse policies. Energy companies also face a significant risk of liability from accidents resulting in injury or loss of life or property, pollution or other environmental problems, equipment malfunctions or mishandling of materials and a risk of loss from terrorism, political strife or natural disasters.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.GLOBAL NATURAL RESOURCES COMPANIES RISK. Investments in global natural resources companies may be affected by numerous factors, including events occurring in nature, inflationary pressures and domestic and international politics. For example, events occurring in nature (such as earthquakes or fires in prime natural resource areas) and political events (such as coups or military confrontations) can affect the overall supply of a natural resource and the value of companies involved in such natural resource. Political risks and other risks to which non-U.S. securities are subject may also affect the U.S. companies in which the Fund invests such companies have significant operations or investments outside of the United States. In addition, interest rates, prices of raw materials and other commodities, international economic developments, energy conservation, tax and other government regulations (both U.S. and non-U.S.) may affect the supply of and demand for natural resources, which can affect the profitability and value of securities issued by global natural resources companies.INDEX CONCENTRATION RISK. The Fund will be concentrated in an industry or a group of industries to the extent that the Index is so concentrated. To the extent that the Fund invests a significant percentage of its assets in a single asset class or the securities of issuers within the same country, state, region, 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. There may be instances in which the Index, for a variety of reasons including changes in the prices of individual securities held by the Fund, has a larger exposure to a small number of stocks or a single stock relative to the rest of the stocks in the Index. Under such circumstances, the Fund will not deviate from the Index except in rare circumstances or in an immaterial way and therefore the Fund’s returns would be more greatly influenced by the returns of the stock(s) with the larger exposure.INDEX OR MODEL CONSTITUENT RISK. The Fund may be a constituent of one or more indices or ETF models. 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.INDEX PROVIDER RISK. There is no assurance that the Index Provider, or any agents that act on its behalf, will compile the Index accurately, or that the Index will be determined, maintained, constructed, reconstituted, rebalanced, composed, calculated or disseminated accurately. The Index Provider and its agents do not provide any representation or warranty in relation to the quality, accuracy or completeness of data in the Index, and do not guarantee that the Index will be calculated in accordance with its stated methodology. The Advisor’s mandate as described in this prospectus is to manage the Fund consistently with the Index provided by the Index Provider. The Advisor relies upon the Index provider and its agents to accurately compile, maintain, construct, reconstitute, rebalance, compose, calculate and disseminate the Index accurately. Therefore, losses or costs associated with any Index Provider or agent errors generally will be borne by the Fund and its shareholders. To correct any such error, the Index Provider or its agents may carry out an unscheduled rebalance of the Index or other modification of Index constituents or weightings. When the Fund in turn rebalances its portfolio, any transaction costs and market exposure arising from such portfolio rebalancing will be borne by the Fund and its shareholders. Unscheduled rebalances also expose the Fund to additional tracking error risk. Errors in respect of the quality, accuracy and completeness of the data used to compile the Index may occur from time to time and may not be identified and corrected by the Index Provider for a period of time or at all, particularly where the Index is less commonly used as a benchmark by funds or advisors. For example, during a period where the Index contains incorrect constituents, the Fund tracking the Index would have market exposure to such constituents and would be underexposed to the Index’s other constituents. Such errors may negatively impact the Fund and its shareholders. The Index Provider and its agents rely on various sources of information to assess the criteria of issuers included in the Index, including information that may be based on assumptions and estimates. Neither the Fund nor the Advisor can offer assurances that the Index’s calculation methodology or sources of information will provide an accurate assessment of included issuers. Unusual market conditions may cause the Index Provider to postpone a scheduled rebalance, which could cause the Index to vary from its normal or expected composition. The postponement of a scheduled rebalance in a time of market volatility could mean that constituents that would otherwise be removed at rebalance due to changes in market capitalizations, issuer credit ratings, or other reasons may remain, causing the performance and constituents of the Index to vary from those expected under normal conditions. Apart from scheduled rebalances, the Index Provider or its agents may carry out additional ad hoc rebalances to the Index due to unusual market conditions or in order, for example, to correct an error in the selection of index constituents.INFLATION RISK. Inflation risk is the risk that the value of assets or income from investments will be less in the future as inflation decreases the value of money. As inflation increases, the present value of the Fund’s assets and distributions may decline.LARGE CAPITALIZATION COMPANIES RISK. Large capitalization companies may grow at a slower rate and be less able to adapt to changing market conditions than smaller capitalization companies. Thus, the return on investment in securities of large capitalization companies may be less than the return on investment in securities of small and/or mid capitalization companies. The performance of large capitalization companies also tends to trail the overall market during different market cycles.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 ensuing policies enacted by governmentsand central banks have caused and may continue to cause significant volatility and uncertainty in global financial markets, negatively impacting global growth prospects. While the U.S. has resumed “reasonably” normal business activity, many countries continue to impose lockdown measures. Additionally, there is no guarantee that vaccines will be effective against emerging variants of the disease. As this global pandemic illustrated, such events may affect certain geographic regions, countries, sectors and industries more significantly than others. These events also 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 and the bid/ask spread on the Fund’s shares may widen.MATERIALS COMPANIES RISK. Materials and processing companies are involved in the extraction or processing of raw materials such as metals, ore and forestry products. These companies are sensitive to changes in the business cycle and fluctuations in the supply and demand for raw materials. Further, certain materials and processing companies can be affected by shifts in the housing market, as many produced raw materials are components of construction projects. Rising wage costs can also impact companies that rely on skilled labor. In addition, materials and processing companies may be significantly affected by volatility of commodity prices, import controls, worldwide competition, liability for environmental damage, depletion of resources and mandated expenditures for safety and pollution control devices.NON-CORRELATION RISK. The Fund’s return may not match the return of the Index for a number of reasons. The Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund’s portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund’s portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index. Additionally, in order to comply with its investment strategies and policies, the Fund portfolio may deviate from the composition of the Index.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.NON-U.S. SECURITIES RISK. Non-U.S. securities are subject to higher volatility than securities of domestic issuers due to possible adverse political, social or economic developments, restrictions on foreign investment or exchange of securities, capital controls, lack of liquidity, currency exchange rates, excessive taxation, government seizure of assets, the imposition of sanctions by foreign governments, different legal or accounting standards, and less government supervision and regulation of securities exchanges in foreign countries.OPERATIONAL RISK. The Fund is subject to risks arising from various operational factors, including, but not limited to, human error, processing and communication errors, errors of the Fund’s service providers, counterparties or other third-parties, failed or inadequate processes and technology or systems failures. The Fund relies on third-parties for a range of services, including custody. Any delay or failure relating to engaging or maintaining such service providers may affect the Fund’s ability to meet its investment objective. Although the Fund and the Fund's investment advisor seek to reduce these operational risks through controls and procedures, there is no way to completely protect against such risks.PASSIVE INVESTMENT RISK. The Fund is not actively managed. The Fund invests in securities included in or representative of the Index regardless of investment merit. The Fund generally will not attempt to take defensive positions in declining markets. In the event that the Index is no longer calculated, the Index license is terminated or the identity or character of the Index is materially changed, the Fund will seek to engage a replacement index.PORTFOLIO TURNOVER RISK. High portfolio turnover may result in the Fund paying higher levels of transaction costs and may generate greater tax liabilities for shareholders. Portfolio turnover risk may cause the Fund’s performance to be less than expected.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 and the bid/ask spread on the Fund’s shares may widen.SMALLER COMPANIES RISK. Small and/or mid 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 larger, more established 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 larger, more established companies.TIMBER COMPANIES RISK. Timber companies may be affected by numerous factors, including events occurring in nature and international politics. For example, the volume and value of timber that can be harvested from timberlands may be limited by natural disasters and other events such as fire, volcanic eruptions, insect infestation, disease, ice storms, wind storms, flooding, other weather conditions and other causes. In periods of poor logging conditions, timber companies may harvest less timber than expected. Timber companies are subject to many federal, state and local environmental and health and safety laws and regulations. In addition, rising interest rates and general economic conditions may affect the demand for timber products.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.WATER COMPANIES RISK. Water companies can be significantly affected by the availability of water, the level of rainfall and the occurrence of other climatic and environmental events, changes in water consumption and water conservation. Water companies may also be negatively affected by changes in governmental regulation and spending, technological advances and increases in inflation, interest rates or the cost of raw materials. Water companies may be subject to liability for environmental damage, depletion of resources, conflicts with local communities over water rights and mandated expenditures for safety and pollution control.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Annual Total Return</span>
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value as well as the average annual Fund and Index returns. The bar chart and table provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual total returns based on net asset value compared to those of the Index, a broad-based market index and a market index. See “Total Return Information” for additional performance information regarding the Fund. The Fund’s performance information is accessible on the Fund’s website at www.ftportfolios.com.On December 18, 2015, the Fund’s underlying index changed from the ISE Global CopperTM Index to the Indxx Global Natural Resources Income Index. Therefore, the Fund’s performance and historical returns shown below are not necessarily indicative of the performance that the Fund, based on the Index, would have generated. Returns for an underlying index are only disclosed for those periods in which the index was in existence for the whole period. Because the Fund’s new underlying index had an inception date of June 1, 2015, it was not in existence for any of the periods disclosed.
Bar Chart [Heading]	rr_BarChartHeading	<span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">First Trust Indxx Global Natural Resources Income ETF</span> <br/><span style="font-family:Arial;font-size:9.90pt;font-weight:bold;margin-left:0%;">Calendar Year Total Returns as of 12/31</span>
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the periods shown in the chart above:Best QuarterWorst Quarter23.65%December 31, 2020-33.65%September 30, 2015
Performance Table Heading	rr_PerformanceTableHeading	<span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">Average Annual Total Returns for the Periods Ended December 31, 2022</span>
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax. Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for the market indices do not include expenses, which are deducted from Fund returns, or taxes.Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.
First Trust Indxx Global Natural Resources Income ETF | First Trust Indxx Global Natural Resources Income 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	0.70%	[1]
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	none
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.70%
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 72
3 Years	rr_ExpenseExampleNoRedemptionYear03	224
5 Years	rr_ExpenseExampleNoRedemptionYear05	390
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 871
2013	rr_AnnualReturn2013	(24.92%)
2014	rr_AnnualReturn2014	(16.36%)
2015	rr_AnnualReturn2015	(45.76%)
2016	rr_AnnualReturn2016	21.96%
2017	rr_AnnualReturn2017	12.53%
2018	rr_AnnualReturn2018	(9.03%)
2019	rr_AnnualReturn2019	21.57%
2020	rr_AnnualReturn2020	(1.15%)
2021	rr_AnnualReturn2021	25.89%
2022	rr_AnnualReturn2022	7.94%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	<span style="color:#000000;font-family:Arial;font-size:9.00pt;font-weight:bold;">Best Quarter</span>
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2020
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	23.65%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	<span style="color:#000000;font-family:Arial;font-size:9.00pt;font-weight:bold;">Worst Quarter</span>
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2015
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(33.65%)
1 Year	rr_AverageAnnualReturnYear01	7.94%
5 Years	rr_AverageAnnualReturnYear05	8.24%
10 Years	rr_AverageAnnualReturnYear10	(3.58%)
Since Inception	rr_AverageAnnualReturnSinceInception	(2.17%)
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 11, 2010
First Trust Indxx Global Natural Resources Income ETF | After tax on distributions | First Trust Indxx Global Natural Resources Income ETF
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	4.31%
5 Years	rr_AverageAnnualReturnYear05	5.65%
10 Years	rr_AverageAnnualReturnYear10	(5.29%)
Since Inception	rr_AverageAnnualReturnSinceInception	(3.71%)
First Trust Indxx Global Natural Resources Income ETF | After tax on distributions and sale of fund shares | First Trust Indxx Global Natural Resources Income ETF
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	4.59%
5 Years	rr_AverageAnnualReturnYear05	5.17%
10 Years	rr_AverageAnnualReturnYear10	(3.37%)
Since Inception	rr_AverageAnnualReturnSinceInception	(2.22%)
First Trust Indxx Global Natural Resources Income ETF | MSCI ACWI Index (reflects no deduction for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(18.36%)
5 Years	rr_AverageAnnualReturnYear05	5.23%
10 Years	rr_AverageAnnualReturnYear10	7.98%
Since Inception	rr_AverageAnnualReturnSinceInception	7.67%
First Trust Indxx Global Natural Resources Income ETF | Indxx Global Natural Resources Income Index (reflects no deduction for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	8.75%	[2]
5 Years	rr_AverageAnnualReturnYear05	9.33%	[2]
10 Years	rr_AverageAnnualReturnYear10		[2]
Since Inception	rr_AverageAnnualReturnSinceInception		[2]
First Trust Indxx Global Natural Resources Income ETF | MSCI ACWI Materials Index (reflects no deduction for fees, expenses or taxes)
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(11.60%)
5 Years	rr_AverageAnnualReturnYear05	4.36%
10 Years	rr_AverageAnnualReturnYear10	4.32%
Since Inception	rr_AverageAnnualReturnSinceInception	3.82%

[1] Effective November 1, 2022, as approved by the Trust’s Board of Trustees, the management fee paid to First Trust Advisors L.P., the Fund's investment advisor, will be reduced at certain levels of Fund net assets (“breakpoints”). See the Fund's Statement of Additional Information for more information on the breakpoints.

[2] Effective on the close of business on December 18, 2015, the Fund's underlying index changed from the ISE Global CopperTM Index to the Indxx Global Natural Resources Income Index. Therefore, the Fund's performance and total returns shown for the period prior to December 18, 2015, are not necessarily indicative of the performance of the Fund, based on its current index, would have generated. Since the Fund's new underlying index had an inception date of June 1, 2015, it was not in existence for all of the periods disclosed.