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Investment Risks - FT Vest Gold Strategy Quarterly Buffer ETF
Dec. 31, 2024
Absence Of An Active Market Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] ABSENCE OF AN ACTIVE MARKET 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 makers or authorized participants. The Fund may rely on a small number of third-party market makers to provide a market for the purchase and sale of shares and market makers are under no obligation to make a market in the Fund’s shares. Additionally, only a limited number of institutions act as authorized participants for the Fund and only an authorized participant may engage in creation or redemption transactions directly with the Fund and are not obligated to submit purchase or redemption orders for Creation Units. 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. Any trading halt or other problem relating to the trading activity of these market makers or any issues disrupting the authorized participants’ ability to proceed with creation and/or redemption orders 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 premium or discount to net asset value and also in greater than normal intraday bid-ask spreads for Fund shares.
Buffered Loss Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] BUFFERED LOSS RISK. There can be no guarantee that the Fund will be successful in its strategy to buffer against Underlying ETF losses if the Underlying ETF decreases over the Target Outcome Period by -5% to -15%. A shareholder may lose their entire investment. The Fund’s strategy seeks to deliver returns that match the price return of the Underlying ETF (up to the cap), while limiting downside losses, if shares are bought on the first day of the Target Outcome Period and held until the end of the Target Outcome Period. In the event an investor purchases shares after the first day of the Target Outcome Period or sells shares prior to the end of the Target Outcome Period, the buffer that the Fund seeks to provide may not be available. If an investor purchases Fund shares during a Target Outcome Period at a time when the Fund has decreased in value by 15% or more from the value of the Fund on the first day of the Target Outcome Period (the “Initial Fund Value”), that investor’s buffer will essentially be zero (meaning the investor can lose its entire investment). If an investor purchases Fund shares at a time when the Fund has decreased in value by more than 5% but less than 15% from the Initial Fund Value, that investor’s buffer will be reduced by the difference between -5% and the NAV of the Fund on the date the investor purchases the shares. An investor that holds Fund shares through multiple Target Outcome Periods will be unable to recapture losses from prior Target Outcome Periods because at the end of each Target Outcome Period, a new buffer will be established based on the then current price of the Underlying ETF and any losses experienced below the prior buffer will be locked in.
Cap Change Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] CAP CHANGE RISK. A new cap is established at the beginning of each Target Outcome Period and is dependent on prevailing market conditions. As a result, the cap may rise or fall from one Target Outcome Period to the next and is unlikely to remain the same for consecutive Target Outcome Periods.
Capped Upside Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] CAPPED UPSIDE RISK. The Fund’s strategy seeks to provide returns (before fees and expenses) that match those of the Underlying ETF for Fund shares purchased on the first day of a Target Outcome Period and held for the entire Target Outcome Period, subject to a pre-determined upside cap. If an investor does not hold its Fund shares for an entire Target Outcome Period, the returns realized by that investor likely will not match those that the Fund seeks to achieve. If the Underlying ETF experiences gains during a Target Outcome Period, the Fund will not participate in those gains beyond the cap. In the event an investor purchases Fund shares after the first day of a Target Outcome Period and the Fund has risen in value to a level near to the cap, there may be little or no ability for that investor to experience an investment gain on their Fund shares (because the investor’s potential gain will be limited to the difference between the Fund’s NAV on the date the investor purchased the Fund shares and the cap), however, the investor will remain vulnerable to downside risks. If an investor buys Fund shares when the price exceeds the cap, an investor will not experience any gain regardless of the performance of the Underlying ETF. An investor that holds Fund shares through multiple Target Outcome Periods may fail to experience gains comparable to those of the Underlying ETF over time because at the end of each Target Outcome Period, a new cap will be established based on the then current price of the Underlying ETF and any gains above the prior cap will be forfeit. Moreover, the quarterly imposition of a new cap on future gains may make it difficult to recoup any losses from prior Target Outcome Periods such that, over multiple Target Outcome Periods, the Fund may have losses that exceed those of the Underlying ETF.
Cash Transactions Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] CASH TRANSACTIONS RISK. The Fund will effect some or all of its creations and redemptions for cash rather than in-kind. As a result, an investment in the Fund may be less tax-efficient than an investment in an ETF that effects its creations and redemptions only in-kind. ETFs are able to make in-kind redemptions and avoid being taxed on gains on the distributed portfolio securities at the fund level. A Fund that effects redemptions for cash may be required to sell portfolio securities in order to obtain the cash needed to distribute redemption proceeds. Any recognized gain on these sales by the Fund will generally cause the Fund to recognize a gain it might not otherwise have recognized, or to recognize such gain sooner than would otherwise be required if it were to distribute portfolio securities only in-kind. The Fund intends to distribute these gains to shareholders to avoid being taxed on this gain at the fund level and otherwise comply with the special tax rules that apply to it. This strategy may cause shareholders to be subject to tax on gains they would not otherwise be subject to, or at an earlier date than if they had made an investment in a different ETF. Moreover, cash transactions may have to be carried out over several days if the securities market is relatively illiquid and may involve considerable brokerage fees and taxes. These brokerage fees and taxes, which will be higher than if the Fund sold and redeemed its shares entirely in-kind, will be passed on to those purchasing and redeeming Creation Units in the form of creation and redemption transaction fees. In addition, these factors may result in wider spreads between the bid and the offered prices of the Fund’s shares than for ETFs that distribute portfolio securities in-kind. The Fund’s use of cash for creations and redemptions could also result in dilution to the Fund and increased transaction costs, which could negatively impact the Fund’s ability to achieve its investment objective.
Commodities Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] COMMODITIES RISK. Commodity prices can have significant volatility, and exposure to commodities can cause the value of the Fund’s shares to decline or fluctuate in a rapid and unpredictable manner. The values of physical commodities may be affected by changes in overall market movements, real or perceived inflationary trends, commodity index volatility, changes in interest rates or currency exchange rates, population growth and changing demographics, international economic, political and regulatory developments, and factors affecting a particular region, industry or commodity, such as drought, floods, or other weather conditions, livestock disease, changes in storage costs, trade embargoes, competition from substitute products, transportation bottlenecks or shortages, fluctuations in supply and demand, and tariffs. The commodity markets are subject to temporary distortions or other disruptions due to, among other factors, lack of liquidity, the participation of speculators, and government regulation and other actions.
Counterparty Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] COUNTERPARTY RISK. Fund transactions involving a counterparty are subject to the risk that the counterparty will not fulfill its obligation to the Fund. Counterparty risk may arise because of the counterparty’s financial condition (i.e., financial difficulties, bankruptcy, or insolvency), market activities and developments, or other reasons, whether foreseen or not. A counterparty’s inability to fulfill its obligation may result in significant financial loss to the Fund. The Fund may be unable to recover its investment from the counterparty or may obtain a limited recovery, and/or recovery may be delayed. The OCC acts as guarantor and central counterparty with respect to the FLEX Options. As a result, the ability of the Fund to meet its objective depends on the OCC being able to meet its obligations. In the unlikely event that the OCC becomes insolvent or is otherwise unable to meet its settlement obligations, the Fund could suffer significant losses.
Credit Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] CREDIT RISK. An issuer or other obligated party of a debt security may be unable or unwilling to make dividend, interest and/or principal payments when due. In addition, the value of a debt security may decline because of concerns about the issuer’s ability or unwillingness to make such payments.
Current Market Conditions Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] CURRENT MARKET CONDITIONS RISK. Current market conditions risk is the risk that a particular investment, or shares of the Fund in general, may fall in value due to current market conditions. As a means to fight inflation, the Federal Reserve and certain foreign central banks have raised interest rates; however, the Federal Reserve has begun to lower interest rates and may continue to do so. U.S. regulators have proposed several changes to market and issuer regulations which would directly impact the Fund, and any regulatory changes could adversely impact the Fund’s ability to achieve its investment strategies or make certain investments. Potential future bank failures could result in disruption to the broader banking industry or markets generally and reduce confidence in financial institutions and the economy as a whole, which may also heighten market volatility and reduce liquidity. Additionally, challenges in commercial real estate markets, including high interest rates, declining valuations and elevated vacancies, could have a broader impact on financial markets. The ongoing adversarial political climate in the United States, as well as political and diplomatic events both domestic and abroad, have and may continue to have an adverse impact the U.S. regulatory landscape, markets and investor behavior, which could have a negative impact on the Fund’s investments and operations. The change in administration resulting from the 2024 United States national elections could result in significant impacts to international trade relations, tax and immigration policies, and other aspects of the national and international political and financial landscape, which could affect, among other things, inflation and the securities markets generally. Other unexpected political, regulatory and diplomatic events within the U.S. and abroad may affect investor and consumer confidence and may adversely impact financial markets and the broader economy. For example, ongoing armed conflicts between Russia and Ukraine in Europe and among Israel, Iran, Hamas and other militant groups in the Middle East, have caused and could continue to cause significant market disruptions and volatility within the markets in Russia, Europe, the Middle East and the United States. The hostilities and sanctions resulting from those hostilities have and could continue to have a significant impact on certain Fund investments as well as Fund performance and liquidity. The economies of the United States and its trading partners, as well as the financial markets generally, may be adversely impacted by trade disputes, including the imposition of tariffs, and other matters. For example, the United States has imposed trade barriers and restrictions on China. In addition, the Chinese government is engaged in a longstanding dispute with Taiwan, continually threatening an invasion. If the political climate between the United States and China does not improve or continues to deteriorate, if China were to attempt invading Taiwan, or if other geopolitical conflicts develop or worsen, economies, markets and individual securities may be adversely affected, and the value of the Fund’s assets may go down. A public health crisis and the ensuing policies enacted by governments and central banks may cause significant volatility and uncertainty in global financial markets, negatively impacting global growth prospects. As the COVID-19 global pandemic illustrated, such events may affect certain geographic regions, countries, sectors and industries more significantly than others. Advancements in technology may also adversely impact markets and the overall performance of the Fund. For instance, the economy may be significantly impacted by the advanced development and increased regulation of artificial intelligence. Additionally, cyber security breaches of both government and non-government entities could have negative impacts on infrastructure and the ability of such entities, including the Fund, to operate properly. These events, and any other future events, may adversely affect the prices and liquidity of the Fund’s portfolio investments and could result in disruptions in the trading markets.
Cyber Security Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] CYBER SECURITY RISK. The Fund is susceptible to operational, information security and related 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, any of which could result in a material adverse effect on the Fund or its shareholders. 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. Emerging threats like ransomware or zero-day exploits could also cause disruptions to Fund operations. 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, among many other third-party service providers, can also subject the Fund to many of the same risks associated with direct cyber security breaches. Further, errors, misconduct, or compromise of accounts of employees of the Fund or its third-party service providers can also create material cybersecurity risks. 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. Cyber security incidents may also trigger Fund obligations under data privacy laws, potentially increasing notification and compliance burdens. Cyber security incidents affecting issuers in whose securities the Fund invests may also have a negative impact on the value of the securities of such issuers, and in turn, the value of the Fund.
Debt Securities Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] DEBT SECURITIES RISK. Investments in debt securities subject the holder to the credit risk of the issuer. Credit risk refers to the possibility that the issuer or other obligor of a security will not be able or willing to make payments of interest and principal when due. Generally, the value of debt securities will change inversely with changes in interest rates. To the extent that interest rates rise, certain underlying obligations may be paid off substantially slower than originally anticipated and the value of those securities may fall sharply. During periods of falling interest rates, the income received by the Fund may decline. If the principal on a debt security is prepaid before expected, the prepayments of principal may have to be reinvested in obligations paying interest at lower rates. Debt securities generally do not trade on a securities exchange making them generally less liquid and more difficult to value than common stock.
Derivatives Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] DERIVATIVES RISK. The use of derivative instruments involves risks different from, or possibly greater than, the risks associated with investing directly in securities and other traditional investments. These risks include or may include: (i) the risk that the value of the underlying assets may go up or down; (ii) the risk that the counterparty to a derivative transaction may not fulfill its contractual obligations; (iii) the risk of mispricing or improper valuation of a derivative; (iv) the risk that changes in the value of the derivative may not correlate perfectly with the underlying asset; (v) the risk that a derivative instrument cannot be sold, closed out or replaced quickly at or very close to its fundamental value; (vi) the risk of loss caused by the unenforceability of a party’s obligations under the derivative; and (vii) the risk that a disruption in the financial markets will cause difficulties for all market participants. Derivative prices are highly volatile and may fluctuate substantially during a short period of time. Such prices are influenced by numerous factors that affect the markets, including, but not limited to: changing supply and demand relationships; government programs and policies; national and international political and economic events, changes in interest rates, inflation and deflation and changes in supply and demand relationships. Trading derivative instruments involves risks different from, or possibly greater than, the risks associated with investing directly in securities. Derivative contracts ordinarily have leverage inherent in their terms. The low margin deposits normally required in trading derivatives, including futures contracts, permit a high degree of leverage. Accordingly, a relatively small price movement may result in an immediate and substantial loss. The use of leverage may also cause the Fund to liquidate portfolio positions when it would not be advantageous to do so. The use of leveraged derivatives can magnify potential for gain or loss and, therefore, amplify the effects of market volatility on share price.
Flex Options Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] FLEX OPTIONS RISK. Trading FLEX Options involves risks different from, or possibly greater than, the risks associated with investing directly in securities. The Fund may experience substantial downside from specific FLEX Option positions and certain FLEX Option positions may expire worthless. The FLEX Options are listed on an exchange; however, no one can guarantee that a liquid secondary trading market will exist for the FLEX Options. In the event that trading in the FLEX Options is limited or absent, the value of the Fund's FLEX Options may decrease. In a less liquid market for the FLEX Options, liquidating the FLEX Options may require the payment of a premium (for written FLEX Options) or acceptance of a discounted price (for purchased FLEX Options) and may take longer to complete. A less liquid trading market may adversely impact the value of the FLEX Options and Fund shares and result in the Fund being unable to achieve its investment objective. Less liquidity in the trading of the Fund’s FLEX Options could have an impact on the prices paid or received by the Fund for the FLEX Options in connection with creations and redemptions of the Fund’s shares. Depending on the nature of this impact to pricing, the Fund may be forced to pay more for redemptions (or receive less for creations) than the price at which it currently values the FLEX Options. Such overpayment or under collection may impact the value of the Fund and whether the Fund can satisfy its investment objective. Additionally, in a less liquid market for the FLEX Options, the liquidation of a large number of options may more significantly impact the price. A less liquid trading market may adversely impact the value of the FLEX Options and the value of your investment. The trading in FLEX Options may be less deep and liquid than the market for certain other exchange-traded options, non-customized options or other securities.
Flex Options Valuation Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] FLEX OPTIONS VALUATION RISK. The FLEX Options held by the Fund will be exercisable at the strike price only on their expiration date. Prior to the expiration date, the value of the FLEX Options will be determined based upon market quotations or using other recognized pricing methods. The FLEX Options are also subject to correlation risk, meaning the value of the FLEX Options does not increase or decrease at the same rate as the Underlying ETF (although they generally move in the same direction) or its underlying securities. The value of the FLEX Options prior to the expiration date may vary because of factors other than the value of the Underlying ETF, such as interest rate changes, changing supply and demand, decreased liquidity of the FLEX Options, a change in the actual and perceived volatility of the stock market and the Underlying ETF and the remaining time to expiration. FLEX Option prices may also be highly volatile and may fluctuate substantially during a short period of time. During periods of reduced market liquidity or in the absence of readily available market quotations for the holdings of the Fund, the ability of the Fund to value the FLEX Options becomes more difficult and the judgment of the Fund's investment adviser (employing the fair value procedures approved by the Board of Trustees of the Trust) may play a greater role in the valuation of the Fund's holdings due to reduced availability of reliable objective pricing data. Consequently, while such determinations may be made in good faith, it may nevertheless be more difficult for the Fund to accurately assign a daily value. Under those circumstances, the value of the FLEX Options will require more reliance on the investment adviser’s judgment than that required for securities for which there is an active trading market. This creates a risk of mispricing or improper valuation of the FLEX Options which could impact the value paid for shares of the Fund.
Income Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] INCOME RISK. The Fund’s income may decline when interest rates fall or if there are defaults in its portfolio. This decline can occur because the Fund may subsequently invest in lower-yielding securities as debt securities in its portfolio mature, are near maturity or are called, or the Fund otherwise needs to purchase additional debt securities.
Index Or Model Constituent Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] 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.
Inflation Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] 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.
Interest Rate Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] INTEREST RATE RISK. Interest rate risk is the risk that the value of the debt securities in the Fund’s portfolio will decline because of rising market interest rates. Interest rate risk is generally lower for shorter term debt securities and higher for longer-term debt securities. The Fund may be subject to a greater risk of rising interest rates than would normally be the case during periods of low interest rates. Duration is a reasonably accurate measure of a debt security’s price sensitivity to changes in interest rates and a common measure of interest rate risk. Duration measures a debt security’s expected life on a present value basis, taking into account the debt security’s yield, interest payments and final maturity. In general, duration represents the expected percentage change in the value of a security for an immediate 1% change in interest rates. For example, the price of a debt security with a three-year duration would be expected to drop by approximately 3% in response to a 1% increase in interest rates. Therefore, prices of debt securities with shorter durations tend to be less sensitive to interest rate changes than debt securities with longer durations. Higher sensitivity to interest rates is generally correlated with higher levels of volatility and, therefore, greater risk. As the value of a debt security changes over time, so will its duration.
Management Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] 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, including through the use of technology, automated processes, algorithms, or other management systems, that may not operate as intended or produce the desired result. There can be no guarantee that the Fund will meet its investment objective.
Market Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] MARKET RISK. Market risk is the risk that a particular investment, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by real or perceived adverse economic, political, and regulatory factors 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, market manipulation, government defaults, government shutdowns, regulatory actions, political changes, diplomatic developments, the imposition of sanctions and other similar measures, spread of infectious diseases or other public health issues, recessions, natural disasters, or other events could have a significant negative impact on the Fund and its investments. Any of such circumstances could have a materially negative impact on the value of the Fund’s shares, the liquidity of an investment, and may 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, the bid/ask spread on the Fund’s shares may widen and the returns on investment may fluctuate.
Risk Nondiversified [Member]  
Prospectus [Line Items]  
Risk [Text Block] 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.
Operational Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] 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. These errors or failures may adversely affect the Fund’s operations, including its ability to execute its investment process, calculate or disseminate its NAV or intraday indicative optimized portfolio value in a timely manner, and process creations or redemptions. The Fund relies on third-parties for a range of services, including custody, valuation, administration, transfer services, securities lending and accounting, among many others. 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.
Premium Discount Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] 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.
Significant Exposure Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] SIGNIFICANT EXPOSURE RISK. To the extent that the Fund invests a significant 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.
Subsidiary Investment Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] SUBSIDIARY INVESTMENT RISK. Changes in the laws of the United States and/or the Cayman Islands, under which the Fund and the Subsidiary are organized, respectively, could result in the inability of the Fund to operate as intended and could negatively affect the Fund and its shareholders. The Subsidiary is not registered under the 1940 Act and is not subject to all the investor protections of the 1940 Act. Thus, the Fund, as an investor in the Subsidiary, will not have all the protections offered to investors in registered investment companies.
Target Outcome Period Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] TARGET OUTCOME PERIOD RISK. The Fund’s investment strategy is designed to deliver returns that match the Underlying ETF if Fund shares are bought on the day on which the Fund enters into the FLEX Options (i.e., the first day of a Target Outcome Period) and held until those FLEX Options expire at the end of the Target Outcome Period subject to the cap. In the event an investor purchases Fund shares after the first day of a Target Outcome Period or sells shares prior to the expiration of the Target Outcome Period, the value of that investor’s investment in Fund shares may not be buffered against a decline in the value of the Underlying ETF and may not participate in a gain in the value of the Underlying ETF up to the cap for the investor’s investment period.
Tax Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] TAX RISK. The Fund intends to treat any income it may derive from FLEX Options on the Underlying ETF received by the Subsidiary as “qualifying income” under the provisions of the Internal Revenue Code of 1986, as amended, applicable to “regulated investment companies” (“RICs”). The Internal Revenue Service had issued numerous private letter rulings (“PLRs”) provided to third parties not associated with the Fund or its affiliates (which only those parties may rely on as precedent) concluding that similar arrangements resulted in qualifying income. Many of such PLRs have now been revoked by the Internal Revenue Service. In March of 2019, the Internal Revenue Service published Regulations that concluded that income from a corporation similar to the Subsidiary would be qualifying income, if the income is related to the Fund’s business of investing in stocks or securities. Although the Regulations do not require distributions from the Subsidiary, the Fund intends to cause the Subsidiary to make distributions that would allow the Fund to make timely distributions to its shareholders. The Fund generally will be required to include in its own taxable income the income of the Subsidiary for a tax year, regardless of whether the Fund receives a distribution of the Subsidiary’s income in that tax year, and this income would nevertheless be subject to the distribution requirement for qualification as a regulated investment company and would be taken into account for purposes of the 4% excise tax. The Fund intends to treat any income it may derive from FLEX Options on the Underlying ETF received by the Subsidiary as “qualifying income” for the rules applicable to RICs. Treasury Regulations provide that income from a corporation similar to the Subsidiary is qualifying income, if (i) the income is distributed to the Fund in the same year the Fund is required to recognize the income or (ii) the income is related to the Fund’s business of investing in stocks or securities. The Fund intends to cause the Subsidiary to make distributions that would allow the Fund to meet the first requirement. The Fund generally will be required to recognize the income of the Subsidiary, regardless of whether the Fund receives a distribution of the Subsidiary’s income, and this income would be subject to the distribution requirement for qualification as a RIC and would be taken into account for purposes of the 4% excise tax.If the Fund did not qualify as a RIC for any taxable year and certain relief provisions were not available, the Fund’s taxable income would be subject to tax at the Fund level and to a further tax at the shareholder level when such income is distributed. In such event, in order to re-qualify for taxation as a RIC, the Fund might be required to recognize unrealized gains, pay substantial taxes and interest and make certain distributions. This would cause investors to incur higher tax liabilities than they otherwise would have incurred and would have a negative impact on Fund returns. In such event, the Fund’s Board of Trustees may determine to reorganize or close the Fund or materially change the Fund’s investment objective and strategies. In the event that the Fund fails to qualify as a RIC, the Fund will promptly notify shareholders of the implications of that failure.
Trading Issues Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] 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.
Underlying ETF Concentration Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] UNDERLYING ETF CONCENTRATION RISK. The Underlying ETF may be susceptible to an increased risk of loss, including losses due to adverse events that affect the Underlying ETF's investments more than the market as a whole, to the extent that the Underlying ETF's investments are concentrated in the securities and/or other assets of a particular issuer or issuers, country, group of countries, region, market, industry, group of industries, sector, market segment or asset class.
Underlying ETF Gold Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] UNDERLYING ETF GOLD RISK. The Fund will have exposure to gold through its investments (through the Subsidiary) in FLEX Options on the Underlying ETF, which invests substantially all of its assets in physical gold bullion. The price of gold bullion can be significantly affected by international monetary and political developments such as currency devaluation or revaluation, central bank movements, economic and social conditions within a country, transactional or trade imbalances, or trade or currency restrictions between countries. Physical gold bullion has sales commission, storage, insurance and auditing expenses. Investments in gold generally may be speculative and subject to greater price volatility than investments in other types of assets. The price of metals, such as gold, is related to, among other things, worldwide metal prices and extraction and production costs. Worldwide metal prices may fluctuate substantially over short periods of time, and as a result, the Fund’s share price may be more volatile than other types of investments. There is a risk that some or all of the Underlying ETF’s gold bars held by its custodian or any subcustodian could be lost, damaged or stolen. Access to the Underlying ETF’s gold bars could also be restricted by natural events (such as an earthquake) or human actions (such as a terrorist attack). Any of these events may adversely affect the operations of the Underlying ETF and, consequently, an investment based on the value of the Underlying ETF’s shares. Additionally, the Underlying ETF does not insure its gold and a loss may be suffered with respect to the Underlying ETF’s gold which is not covered by insurance and for which no party is liable for damages.
Underlying ETF Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] UNDERLYING ETF RISK. The Subsidiary invests in FLEX Options that reference an ETF, which subjects the Subsidiary to certain of the risks of owning shares of an ETF as well as the types of instruments in which the Underlying ETF invests. The value of an ETF will fluctuate over time based on fluctuations in the values of the securities held by the ETF, which may be affected by changes in general economic conditions, expectations for future growth and profits, interest rates and the supply and demand for those securities. In addition, ETFs are subject to the absence of an active market risk, premium/discount risk, tracking error risk and trading issues risk. Brokerage, tax and other expenses may negatively impact the performance of the Underlying ETF and, in turn, the value of the Fund’s shares. Certain options on an ETF may not qualify as "Section 1256 contracts" under Section 1256 of the Code, and disposition of such options will likely result in short-term or long-term capital gains or losses depending on the holding period.
US Government Securities Risk [Member]  
Prospectus [Line Items]  
Risk [Text Block] U.S. GOVERNMENT SECURITIES RISK. U.S. government securities are subject to interest rate risk but generally do not involve the credit risks associated with investments in other types of debt securities. As a result, the yields available from U.S. government securities are generally lower than the yields available from other debt securities. U.S. government securities are guaranteed only as to the timely payment of interest and the payment of principal when held to maturity.
Risk Lose Money [Member]  
Prospectus [Line Items]  
Risk [Text Block] You could lose money by investing in the Fund.
Risk Not Insured Depository Institution [Member]  
Prospectus [Line Items]  
Risk [Text Block] 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.