| N-2 | 6 Months Ended |
| Jun. 30, 2023 shares | |
| Cover [Abstract] | |
| Entity Central Index Key | 0000921671 |
| Amendment Flag | false |
| Document Type | N-CSRS |
| Entity Registrant Name | The Gabelli Multimedia Trust Inc. |
| Document Period End Date | Jun. 30, 2023 |
| General Description of Registrant [Abstract] | |
| Investment Objectives and Practices [Text Block] | Investment Objective and Strategy (Unaudited) The Gabelli Multimedia Trust is a non-diversified, closed-end management investment company whose primary objective is long term growth of capital, with income as a secondary objective. The Fund will invest at least 80% of its assets, under normal market conditions, in common stock and other securities, including convertible securities, preferred stock, options, and warrants of companies in the telecommunications, media, publishing, and entertainment industries. |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |
| Capital Stock [Table Text Block] | 6. Capital. Six Months Ended Year Ended Shares Amount Shares Amount Increase in net assets from common shares issued upon reinvestment of distributions 189,631 $ 1,110,831 272,128 $ 1,759,964 The Fund’s Articles of Incorporation authorize the issuance of up to 4,001,000 shares of $0.001 par value Preferred Stock. The Preferred Stock is senior to the common stock and results in the financial leveraging of the common stock. Such leveraging tends to magnify both the risks and opportunities to common stockholders. Dividends on shares of the Preferred Stock are cumulative. The Fund is required by the 1940 Act and by the Articles Supplementary to meet certain asset coverage tests with respect to the Preferred Stock. If the Fund fails to meet these requirements and does not correct such failure, the Fund may be required to redeem, in part or in full, the Series C, Series E, and Series G Preferred at redemption prices of $25,000, $25, and $25, respectively, per share plus an amount equal to the accumulated and unpaid dividends whether or not declared on such shares in order to meet these requirements. Additionally, failure to meet the foregoing asset coverage requirements could restrict the Fund’s ability to pay dividends to common stockholders and could lead to sales of portfolio securities at inopportune times. The income received on the Fund’s assets may vary in a manner unrelated to the fixed and variable rates, which could have either a beneficial or detrimental impact on net investment income and gains available to common stockholders. The Fund has the authority to purchase its auction rate preferred shares through negotiated private transactions. The Fund is not obligated to purchase any dollar amount or number of auction rate preferred shares, and the timing and amount of any auction rate preferred shares purchased will depend on market conditions, share price, capital availability, and other factors. The Fund is not soliciting holders to sell these shares nor recommending that holders offer them to the Fund. Any offers can be accepted or rejected in the Fund’s discretion. For Series C Preferred Stock, the dividend rates, as set by the auction process that is generally held every seven days, are expected to vary with short term interest rates. Since February 2008, the number of shares of Series C Preferred Stock subject to bid orders by potential holders has been less than the number of shares of Series C Preferred Stock subject to sell orders. Holders that have submitted sell orders have not been able to sell any or all of the Series C Preferred Stock for which they have submitted sell orders. Therefore the weekly auctions have failed, and the dividend rate has been the maximum rate, which is 175% of the “AA” Financial Composite Commercial Paper Rate on the day of such auction. Existing Series C stockholders may submit an order to hold, bid, or sell such shares on each auction date, or trade their shares in the secondary market. The Fund may redeem at any time, in whole or in part, the Series C Preferred Stock and Series E Preferred Stock at their respective redemption prices per share. In addition, the Board has authorized the repurchase of the Series E and Series G Preferred Stock in the open market at prices less than the $25 liquidation value per share. During the six months ended June 30, 2023 and the year ended December 31, 2022, the Fund repurchased and retired 36,574 and 184,154 Series E Preferred at investments of $874,326 and $4,402,156, respectively, and at average discounts of approximately 4.42% and 4.42%, from its liquidation preference. During the six months ended June 30, 2023 and the year ended December 31, 2022, the Fund repurchased and retired 29,756 and 368,698 Series G Preferred at investments of $713,569 and 8,822,681, respectively, and at average discounts of approximately 4.25% and 4.32%, respectively, from its liquidation preference. The following table summarizes Cumulative Preferred Stock information: Series Issue Date Authorized Number of Net Proceeds 2023 Dividend Rate Range Dividend Rate at 6/30/2023 Accrued Dividends at 6/30/2023 C Auction Rate March 31, 2003 1,000 10 $ 24,547,465 7.514% to 8.881% 8.881 % $ 182 E 5.125% September 26, 2017 2,000,000 1,775,972 $ 48,192,240 Fixed Rate 5.125 % $ 31,604 G 5.125% December 20, 2019 2,000,000 1,591,747 $ 48,148,000 Fixed Rate 5.125 % $ 28,325 The holders of Preferred Shares generally are entitled to one vote per share held on each matter submitted to a vote of stockholders of the Fund and will vote together with holders of common stock as a single class. The holders of Preferred Shares voting together as a single class also have the right currently to elect two Directors and, under certain circumstances, are entitled to elect a majority of the Board of Directors. In addition, the affirmative vote of a majority of the votes entitled to be cast by holders of all outstanding shares of the preferred shares, voting as a single class, will be required to approve any plan of reorganization adversely affecting the preferred stock, and the approval of two-thirds of each class, voting separately, of the Fund’s outstanding voting stock must approve the conversion of the Fund from a closed-end to an open-end investment company. The approval of a majority (as defined in the 1940 Act) of the outstanding preferred shares and a majority (as defined in the 1940 Act) of the Fund’s outstanding voting securities are required to approve certain other actions, including changes in the Fund’s investment objectives or fundamental investment policies. |
| Common Stocks [Member] | |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |
| Outstanding Security, Not Held [Shares] | 27,893,139 |
| Cumulative Preferred Stocks [Member] | |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |
| Security Voting Rights [Text Block] | The holders of Preferred Shares generally are entitled to one vote per share held on each matter submitted to a vote of stockholders of the Fund and will vote together with holders of common stock as a single class. The holders of Preferred Shares voting together as a single class also have the right currently to elect two Directors and, under certain circumstances, are entitled to elect a majority of the Board of Directors. In addition, the affirmative vote of a majority of the votes entitled to be cast by holders of all outstanding shares of the preferred shares, voting as a single class, will be required to approve any plan of reorganization adversely affecting the preferred stock, and the approval of two-thirds of each class, voting separately, of the Fund’s outstanding voting stock must approve the conversion of the Fund from a closed-end to an open-end investment company. The approval of a majority (as defined in the 1940 Act) of the outstanding preferred shares and a majority (as defined in the 1940 Act) of the Fund’s outstanding voting securities are required to approve certain other actions, including changes in the Fund’s investment objectives or fundamental investment policies. |
| Preferred Stock Restrictions, Other [Text Block] | The Fund’s Articles of Incorporation authorize the issuance of up to 4,001,000 shares of $0.001 par value Preferred Stock. The Preferred Stock is senior to the common stock and results in the financial leveraging of the common stock. Such leveraging tends to magnify both the risks and opportunities to common stockholders. Dividends on shares of the Preferred Stock are cumulative. The Fund is required by the 1940 Act and by the Articles Supplementary to meet certain asset coverage tests with respect to the Preferred Stock. If the Fund fails to meet these requirements and does not correct such failure, the Fund may be required to redeem, in part or in full, the Series C, Series E, and Series G Preferred at redemption prices of $25,000, $25, and $25, respectively, per share plus an amount equal to the accumulated and unpaid dividends whether or not declared on such shares in order to meet these requirements. Additionally, failure to meet the foregoing asset coverage requirements could restrict the Fund’s ability to pay dividends to common stockholders and could lead to sales of portfolio securities at inopportune times. The income received on the Fund’s assets may vary in a manner unrelated to the fixed and variable rates, which could have either a beneficial or detrimental impact on net investment income and gains available to common stockholders. The Fund has the authority to purchase its auction rate preferred shares through negotiated private transactions. The Fund is not obligated to purchase any dollar amount or number of auction rate preferred shares, and the timing and amount of any auction rate preferred shares purchased will depend on market conditions, share price, capital availability, and other factors. The Fund is not soliciting holders to sell these shares nor recommending that holders offer them to the Fund. Any offers can be accepted or rejected in the Fund’s discretion. For Series C Preferred Stock, the dividend rates, as set by the auction process that is generally held every seven days, are expected to vary with short term interest rates. Since February 2008, the number of shares of Series C Preferred Stock subject to bid orders by potential holders has been less than the number of shares of Series C Preferred Stock subject to sell orders. Holders that have submitted sell orders have not been able to sell any or all of the Series C Preferred Stock for which they have submitted sell orders. Therefore the weekly auctions have failed, and the dividend rate has been the maximum rate, which is 175% of the “AA” Financial Composite Commercial Paper Rate on the day of such auction. Existing Series C stockholders may submit an order to hold, bid, or sell such shares on each auction date, or trade their shares in the secondary market. The Fund may redeem at any time, in whole or in part, the Series C Preferred Stock and Series E Preferred Stock at their respective redemption prices per share. In addition, the Board has authorized the repurchase of the Series E and Series G Preferred Stock in the open market at prices less than the $25 liquidation value per share. During the six months ended June 30, 2023 and the year ended December 31, 2022, the Fund repurchased and retired 36,574 and 184,154 Series E Preferred at investments of $874,326 and $4,402,156, respectively, and at average discounts of approximately 4.42% and 4.42%, from its liquidation preference. During the six months ended June 30, 2023 and the year ended December 31, 2022, the Fund repurchased and retired 29,756 and 368,698 Series G Preferred at investments of $713,569 and 8,822,681, respectively, and at average discounts of approximately 4.25% and 4.32%, respectively, from its liquidation preference. |
| Outstanding Securities [Table Text Block] | The following table summarizes Cumulative Preferred Stock information: Series Issue Date Authorized Number of Net Proceeds 2023 Dividend Rate Range Dividend Rate at 6/30/2023 Accrued Dividends at 6/30/2023 C Auction Rate March 31, 2003 1,000 10 $ 24,547,465 7.514% to 8.881% 8.881 % $ 182 E 5.125% September 26, 2017 2,000,000 1,775,972 $ 48,192,240 Fixed Rate 5.125 % $ 31,604 G 5.125% December 20, 2019 2,000,000 1,591,747 $ 48,148,000 Fixed Rate 5.125 % $ 28,325 |
| Series C Cumulative Preferred Stock [Member] | |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |
| Outstanding Security, Title [Text Block] | C Auction Rate |
| Outstanding Security, Authorized [Shares] | 1,000 |
| Outstanding Security, Not Held [Shares] | 10 |
| Series E Cumulative Preferred Stock [Member] | |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |
| Outstanding Security, Title [Text Block] | E 5.125% |
| Outstanding Security, Authorized [Shares] | 2,000,000 |
| Outstanding Security, Not Held [Shares] | 1,775,972 |
| Series G Cumulative Preferred Stock [Member] | |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |
| Outstanding Security, Title [Text Block] | G 5.125% |
| Outstanding Security, Authorized [Shares] | 2,000,000 |
| Outstanding Security, Not Held [Shares] | 1,591,747 |
