| N-2 - $ / shares | 12 Months Ended | |||||
| Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019 | |
| Prospectus [Line Items] | ||||||
| Document Period End Date | Sep. 30, 2024 | |||||
| Cover [Abstract] | ||||||
| Entity Central Index Key | 0001467631 | |||||
| Amendment Flag | false | |||||
| Document Type | N-CSR | |||||
| Entity Registrant Name | ACAP Strategic Fund | |||||
| Other Transaction Expenses [Abstract] | ||||||
| Management Fees [Percent] | 1.50% | |||||
| Incentive Fees [Percent] | 20% | |||||
| General Description of Registrant [Abstract] | ||||||
| Investment Objectives and Practices [Text Block] | The Fund’s investment objective is to achieve maximum capital appreciation. The Fund pursues this objective by investing its assets primarily in publicly-traded equity securities of U.S. and foreign companies that the Adviser believes are well positioned to benefit from demand for their products or services, including companies that can innovate or grow rapidly relative to their peers in their markets. The Fund also pursues its objective by effecting short sales of securities when the Adviser believes that the market price of a security is above its estimated intrinsic or fundamental value. The Fund may also borrow money for investment purposes (leverage). The use of short sales and leverage are speculative investment practices and involve a high degree of risk. | |||||
| Risk [Text Block] | 11. Principal and Non-Principal Fund Investment Practices and Their Risks Although the Fund’s principal investment strategy is to invest primarily in publicly traded equity securities of U.S. and foreign companies, the Fund may invest its assets in other types of securities and in other asset classes when, in the judgment of the Adviser (subject to any policies established by the Board), such investments present opportunities for the Fund to achieve maximum capital appreciation, taking into account the availability of equity investment opportunities, market conditions, the relative risk/reward analysis of other investments compared to equity securities, and such other considerations as the Adviser deems appropriate. The Fund may effect short sales of securities when the Adviser believes that the market price of a security is above its estimated intrinsic or fundamental value. For example, the Fund may “short” a security of a company if the Adviser believes the security is over-valued in relation to the issuer’s prospects for earnings growth. In addition, the Fund may attempt to limit exposure to a possible market decline in the value of its portfolio securities through short sales of securities that the Adviser believes possess volatility characteristics similar to those being hedged. At times, the Fund may be exposed significantly to short positions and, as a result, the dollar value of short positions in the portfolio could exceed the dollar value of long positions. To effect a short sale, the Fund will borrow a security from a brokerage firm to make delivery to the buyer. The Fund is then obligated to replace the borrowed security by purchasing it at the market price at the time of replacement. Thus, short sales expose the Fund to the risk that it will be required to buy the security sold short (also known as “covering” the short position) at a time when the security has appreciated in value, thus resulting in a loss to the Fund. Positions in stocks sold short are more risky than long positions (purchases) in stocks because the maximum loss on a stock purchased is limited to the amount paid for the stock plus the transaction costs, where in the case of a short sale, there is no limit on the loss that may be incurred. The Fund is required to pay the lender any dividends declared on short positions. Such amounts are recorded on the ex-dividend date as Dividends on securities sold, not yet purchased on the Statement of Operations. In accordance with the terms of its prime brokerage agreement, the Funds may be charged a fee on borrowed securities. Such fees are calculated on a daily basis based upon the market value of each borrowed security and a variable rate that is dependent upon the availability of such security. The fees are presented as Stock loan fees on the Statement of Operations. There is a risk that the borrowed securities would need to be returned to the brokerage firm on short notice. If a request for return of securities occurs at a time when other short sellers of the subject security are receiving similar requests, a “short squeeze” can occur, and the Fund might be compelled, at the most disadvantageous time, to replace borrowed securities previously sold short with purchases on the open market, possibly at prices significantly in excess of the price at which the securities were sold short. The successful use of short selling may be adversely affected by imperfect correlation between movements in the price of the security sold short and the securities being hedged. Short selling may exaggerate the volatility of the Fund’s investment portfolio. Short selling may also produce higher than normal portfolio turnover and may result in increased transaction costs to the Fund. In addition, the Fund, as a result of certain short sale transactions, may recognize short term capital gain. The Fund’s short sales have the effect of leveraging the Fund’s assets. The Fund may also generate leverage through engaging in securities lending. The Fund’s use of total return swaps can also expose the Fund to leveraged investment exposure. During periods of volatility, regulators may impose certain restrictions or disclosure requirements on short sales. The levels of restriction and disclosure may vary across different jurisdictions. Such restrictions and disclosure requirements may make it difficult for the Adviser to express its negative views in relation to certain securities, companies or sectors, which may have an adverse effect on the Fund’s ability to implement its investment strategy. Authoritative guidance on disclosures about derivative instruments and hedging activities requires qualitative disclosures about objectives and strategies for using derivatives, quantitative disclosures about fair value amounts of gains and losses on derivative instruments and disclosures about credit-risk-related contingent features in derivative agreements. The realized gain/(loss) on swap contracts and foreign currency transactions is reflected on the Statement of Operations within these financial statements. The net change in unrealized appreciation/ depreciation on swap contracts is reflected on the Statement of Operations within these financial statements. The net change in unrealized appreciation/depreciation on foreign currency transactions is reflected on the Statement of Operations within these financial statements as a component of the net change in unrealized appreciation/ depreciation from investment activities and foreign currency transactions. Option contracts serve as components of the Fund’s investment strategies and are utilized to structure investments to enhance the performance of the Fund. Foreign (Non-U.S.) Risk – Investments in securities of non-U.S. issuers may involve more risk than those of U.S. issuers. These securities may fluctuate more widely in price and may be less liquid due to adverse market, economic, political, regulatory or other factors, including as a result of wars such as in the Ukraine and the Middle East. a. Bonds and Other Fixed-Income Securities The Fund may invest without limit in high quality fixed-income securities for temporary defensive purposes and to maintain liquidity. For these purposes, “fixed-income securities” are bonds, notes and debentures issued by corporations; debt securities issued or guaranteed by the U.S. Government or one of its agencies or instrumentalities (“U.S. Government Securities”) or by a foreign government; municipal securities; and mortgage-backed and asset-backed securities. These securities may pay fixed, variable or floating rates of interest, and may include zero coupon obligations. Fixed-income securities are subject to the risk of the issuer’s inability to meet principal and interest payments on its obligations (i.e., credit risk) and are subject to price volatility due to such factors as interest rate sensitivity, market perception of the credit worthiness of the issuer and general market liquidity (i.e., market risk). The Fund may also invest in both investment grade and non-investment grade debt securities. Investment grade debt securities are securities that have received a rating from at least one nationally recognized statistical rating organization (“NRSRO”) in one of the four highest rating categories or, if not rated by any NRSRO, have been determined by the Adviser to be of comparable quality. The Fund may also invest in convertible bonds. Non-investment grade debt securities (typically called “junk bonds”) are securities that have received a rating from an NRSRO of below investment grade or have been given no rating, and are considered by the NRSRO to be predominantly speculative with respect to the issuer’s capacity to pay interest and repay principal. Non-investment grade debt securities in the lowest rating categories may involve a substantial risk of default or may be in default. Adverse changes in economic conditions or developments regarding the individual issuer are more likely to cause price volatility and weaken the capacity of the issuers of non-investment grade debt securities to make principal and interest payments than is the case for higher grade debt securities. An economic downturn affecting an issuer of non-investment grade debt securities may result in an increased incidence of default. In addition, the market for lower grade debt securities may be thinner and less active than for higher grade debt securities. The Fund does not expect to invest more than 15% of its net assets in non-convertible debt securities. The Fund’s investments in non-investment grade debt securities, if any, are not expected to exceed 5% of its net assets. At September 30, 2024, the Fund held no positions of the above-mentioned investments. b. Exchange Traded Funds and Other Similar Instruments The Fund may purchase retail shares of exchange-traded funds (“ETFs”) that are registered under the 1940 Act and retail shares of similar investment vehicles that are not registered under the 1940 Act (together with the ETFs, “Traded Funds”) and effect short sales of these shares. Transactions in Traded Funds may be used in seeking maximum capital appreciation or for hedging purposes. Typically, a Traded Fund holds a portfolio of common stocks designed to track the performance of a particular index or a “basket” of stocks of companies within a particular industry sector or group. Traded Funds sell and redeem their shares at net asset value in large blocks (typically 50,000 shares) called “creation units.” Shares representing fractional interests in these creation units are listed for trading on national securities exchanges and can be purchased and sold in the secondary market in lots of any size at any time during the trading day (i.e., retail shares). Investments in Traded Funds involve certain inherent risks generally associated with investments in a broadly-based portfolio of stocks including risks that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the Traded Funds. In addition, a Traded Fund may not fully replicate the performance of its benchmark index because of the temporary unavailability of certain index securities in the secondary market or discrepancies between the Traded Fund and the index with respect to the weighting of securities or number of stocks held. Because Traded Funds bear various fees and expenses, the Fund’s investment in these instruments will involve certain indirect costs, as well as transaction costs, such as brokerage commissions. The Adviser considers the expenses associated with an investment in determining whether to invest in a Traded Fund. At September 30, 2024, the Fund held no positions of the above-mentioned investments. c. Temporary Investments; U.S. Government Securities Risk During periods of adverse market conditions in the equity securities markets, the Fund may deviate from its investment objective and invest all or a portion of its assets in high quality debt securities, money market instruments, or hold its assets in cash. Securities will be deemed to be of high quality if they are rated in the top four categories by an NRSRO or, if unrated, are determined to be of comparable quality by the Adviser. Money market instruments are high quality, short-term debt obligations (which generally have remaining maturities of one year or less), and may include: U.S. Government Securities; commercial paper; certificates of deposit and banker’s acceptances issued by domestic branches of United States banks that are members of the Federal Deposit Insurance Corporation (“FDIC”); and repurchase agreements for U.S. Government Securities. In lieu of purchasing money market instruments, the Fund may purchase shares of money market mutual funds that invest primarily in U.S. Government Securities and repurchase agreements involving those securities, subject to certain limitations imposed by the 1940 Act. The Fund may also invest in money market instruments or purchase shares of money market mutual funds pending investment of its assets in equity securities or non-money market debt securities, or to maintain such liquidity as may be necessary to effect repurchases of shares from shareholders or for other purposes. It is possible that the U.S. Government would not provide financial support to its agencies or instrumentalities if it were not required to do so by law. If a U.S. Government agency or instrumentality in which the Fund invests defaults and the U.S. Government does not stand behind the obligation, the Fund’s Share price or yield could fall. The U.S. Government’s guarantee of ultimate payment of principal and timely payment of interest of the U.S. Government Securities owned by the Fund does not imply that the Fund’s Shares are guaranteed by the FDIC or any other government agency, or that the price of the Fund’s Shares will not continue to fluctuate. At September 30, 2024, the fair value of the above-mentioned investments was $137,807,477 and is presented as part of investments in securities on the Statement of Assets and Liabilities. d. Total Return Swaps The Adviser may use total return swaps to pursue the Fund’s investment objective of maximum capital appreciation. The Adviser may also use these swaps for hedging purposes. A swap is a contract under which two parties agree to make periodic payments to each other based on specified interest rates, an index or the value of some other instrument, applied to a stated notional amount. Swaps generally can be classified as interest rate swaps, currency swaps, commodity swaps, total return swaps or equity swaps, depending on the type of index or instrument used to calculate the payments. Such swaps would increase or decrease the Fund’s investment exposure to the particular interest rate, currency, commodity or equity involved. Total return swap agreements are contracts in which one party agrees to make periodic payments based on the change in market value of underlying assets, which may include a specified security, basket of securities, defined portfolios of bonds, loans and mortgages, or securities indexes during the specified period, in return for periodic payments based on a fixed or variable interest rate or the total return of other underlying assets or indices. Total return swap agreements may be used to obtain exposure to a security or market without owning or taking physical custody of such security index or market. Most swap agreements entered into by the Fund require the calculation of the obligations of the parties to the agreements on a “net basis.” Consequently, current obligations (or rights) under a swap agreement generally will be equal to only the net amount to be paid or received under the agreement based on the relative values of the positions held by each party to the agreement (the “net amount”). The Fund’s current obligations under a swap agreement will be accrued daily (offset against amounts owed to the Fund), and any accrued but unpaid net amounts owed to a swap counterparty will be covered in accordance with applicable regulatory requirements. Obligations under swap agreements so covered will not be construed to be “senior securities” for purposes of the Fund’s investment restriction concerning senior securities. The Fund is subject to the market risk associated with changes in the value of the underlying investment or instrument, as well as exposure to credit risk associated with counterparty non-performance on swap contracts. The risk of loss with respect to swaps is limited to the net amount of payments that the Fund is contractually obligated to make. If the other party to a swap defaults, the Fund’s risk of loss generally consists of the net amount of payments that the Fund contractually is entitled to receive and/or the termination value at the end of the contract, which may be different than the amounts recorded on the Statement of Assets and Liabilities. Total return swaps are non-income producing instruments. The Fund’s total return swap contract counterparty is Morgan Stanley & Co., Inc. At September 30, 2024, the net amount of the fair value of the above-mentioned investments was $314,557,837 and is presented as net unrealized appreciation on total return swap contracts on the Statement of Assets and Liabilities. e. Call and Put Options on Individual Securities The Fund may purchase call and put options in respect of specific securities, and may write and sell covered or uncovered call and put options for hedging purposes and non-hedging purposes to pursue its investment objective. A put option gives the purchaser of the option the right to sell, and obligates the writer to buy, the underlying security at a stated exercise price at any time prior to the expiration of the option. Similarly, a call option gives the purchaser of the option the right to buy, and obligates the writer to sell, the underlying security at a stated exercise price at any time prior to the expiration of the option. A covered call option written by the Fund is a call option with respect to which the Fund owns the underlying security. A covered put option written by the Fund is a put option with respect to which cash or liquid securities have been placed in a segregated account on the Fund’s books or with the Fund’s custodian to fulfill the obligation undertaken. The Fund may close out a position when writing options by purchasing an option on the same security with the same exercise price and expiration date as the option that it has previously written on the security. The Fund will realize a profit or loss if the amount paid to purchase an option is less or more, as the case may be, than the amount received from the sale thereof. To close out a position as a purchaser of an option, the Fund would ordinarily make a similar “closing sale transaction,” which involves liquidating the Fund’s position by selling the option previously purchased, although the Fund would be entitled to exercise the option should it deem it advantageous to do so. The Fund may also invest in so-called “synthetic” options or other derivative instruments written by broker-dealers. Options transactions may be effected on securities exchanges or in the over-the-counter market. Over-the-counter options purchased and sold by the Fund may also include options on baskets of specific securities. The use of options is a highly specialized activity which involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. The Fund may buy and sell call and put options, including options on currencies. If the Fund sells a put option, there is a risk that the Fund may be required to buy the underlying asset at a disadvantageous price. If the Fund sells a call option, there is a risk that the Fund may be required to sell the underlying asset at a disadvantageous price, and if the call option sold is not covered (for example, by owning the underlying asset), the Fund’s losses are potentially unlimited. Options may be traded over-the-counter or on a securities exchange. These transactions involve risks consisting of counterparty credit risk and leverage risk. At September 30, 2024, the fair value of the above-mentioned investments was $992,538,879 and is presented as part of purchased options on the Statement of Assets and Liabilities. f. Foreign Currency Transactions Portfolio securities and other assets and liabilities denominated in foreign currencies are translated into U.S. dollars based on the exchange rate of such currencies against U.S. dollars on the date of valuation. The Fund may enter into foreign currency exchange contracts to facilitate transactions denominated in a foreign currency. Purchases and sales of securities and income and expense items denominated in foreign currencies are translated into U.S. dollars at the exchange rate in effect on the transaction date. Occasionally, events may impact the availability or reliability of foreign exchange rates used to convert the U.S. dollar equivalent value. If such an event occurs, the foreign exchange rate will be valued at fair value using procedures established and approved by the Board. The Fund does not separately report the effect of changes in foreign exchange rates from changes in market prices on securities held. Such changes are included in the net change in unrealized appreciation/depreciation from investment activities and foreign currency transactions and in net realized gain/(loss) from investment activities on the Statement of Operations. Realized foreign exchange gains or losses arise from sales of foreign currencies, currency gains or losses realized between the trade and settlement dates on securities transactions and the difference between the recorded amounts of dividends, interest, and foreign withholding taxes and the U.S. dollar equivalent of the amounts actually received or paid. Net unrealized foreign exchange gains and losses arise from changes in foreign exchange rates on foreign denominated assets and liabilities other than investments in securities held at the end of the reporting period. The Fund may enter into forward contracts for hedging and non-hedging purposes to pursue its investment objective. These contracts represent obligations to purchase or to sell a specified amount of currency at a future date and at a specified price agreed to by the parties at the time they enter into the contracts and allow the Fund to “lock in” the U.S. dollar prices of securities. However, there may be an imperfect correlation between the securities being purchased or sold and the forward contracts entered into, and there is a risk that a counterparty will be unable or unwilling to fulfill its obligations under the forward contract. At September 30, 2024, the Fund held no positions of the above-mentioned investments. The Fund may also seek to hedge against the decline in the value of a currency or, to the extent applicable, to enhance returns, through the use of currency options. Currency options are similar to options on securities. For example, in consideration for an option premium the writer of a currency option is obligated to sell (in the case of a call option) or purchase (in the case of a put option) a specified amount of a specified currency on or before the expiration date for a specified amount of another currency. The Fund may engage in transactions in options on currencies either on exchanges or over-the-counter markets. Currency options involve substantial currency risk, and may also involve credit, leverage or liquidity risk. At September 30, 2024, the fair value of the currency options was $9,841,514 and is presented as part of purchased options on the Statement of Assets and Liabilities. | |||||
| Effects of Leverage [Text Block] | The Fund’s short sales have the effect of leveraging the Fund’s assets. The Fund may also generate leverage through engaging in securities lending. The Fund’s use of total return swaps can also expose the Fund to leveraged investment exposure. During periods of volatility, regulators may impose certain restrictions or disclosure requirements on short sales. The levels of restriction and disclosure may vary across different jurisdictions. Such restrictions and disclosure requirements may make it difficult for the Adviser to express its negative views in relation to certain securities, companies or sectors, which may have an adverse effect on the Fund’s ability to implement its investment strategy. | |||||
| Effects of Leverage, Purpose [Text Block] | Although leverage can increase investment returns if the Fund earns a greater return on the investments purchased with borrowed funds than it pays for the use of those funds, the use of leverage will decrease investment returns if the Fund fails to earn as much on investments purchased with borrowed funds as it pays for the use of those funds. The use of leverage will therefore magnify the impact of changes in the value of investments held by the Fund on the Fund’s net asset value and thus can increase the volatility of the Fund’s net asset value per Share. The Fund’s investment program makes frequent use of leverage. | |||||
| Class A [Member] | ||||||
| Fee Table [Abstract] | ||||||
| Sales Load [Percent] | 3% | |||||
| General Description of Registrant [Abstract] | ||||||
| Annual Dividend Payment | $ (0.40) | $ (1.06) | $ (0.65) | |||
| NAV Per Share | $ 22.51 | 16.21 | 14.22 | 24.72 | 25.49 | $ 17.84 |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | ||||||
| Outstanding Security, Held [Shares] | 286,918,171 | |||||
| Class W [Member] | ||||||
| General Description of Registrant [Abstract] | ||||||
| Annual Dividend Payment | (0.40) | (1.06) | (0.65) | |||
| NAV Per Share | $ 16.97 | $ 12.13 | $ 10.56 | $ 18.33 | $ 19.02 | $ 13.37 |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | ||||||
| Outstanding Security, Held [Shares] | 125,838,180 | |||||
