| Form N-CSR Cover | 12 Months Ended |
| Sep. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | Investment Managers Series Trust III |
| Entity Central Index Key | 0000924727 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Sep. 30, 2024 |
| Shareholder Report | 12 Months Ended |
| Sep. 30, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | Investment Managers Series Trust III |
| Entity Central Index Key | 0000924727 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Sep. 30, 2024 |
| C000247942 [Member] | |
| Shareholder Report [Line Items] | |
| Fund Name | FPA Global Equity ETF |
| Class Name | FPA Global Equity ETF |
| Trading Symbol | FPAG |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the FPA Global Equity ETF (“Fund”) for the period of October 1, 2023 to September 30, 2024. |
| Shareholder Report Annual or Semi-Annual | annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at https://fpag.fpa.com/ |
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during the reporting period. |
| Additional Information Phone Number | (800) 982-4372 |
| Additional Information Website | https://fpag.fpa.com/ |
| Expenses [Text Block] | Fund Expenses (Based on a hypothetical $10,000 investment) Fund (Class) Costs of a $10,000 investment Costs paid as a percentage FPA Global Equity ETF $ 0.49 % |
| Expenses Paid, Amount | $ 57 |
| Expense Ratio, Percent | 0.49% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The FPA Global Equity ETF (“Fund” or “FPAG”) gained 31.24%, net, in the trailing twelve months (“TTM”). The MSCI ACWI Index returned 31.76% for the same period. The Fund captured 98.4% of the MSCI ACWI’s return in the trailing twelve months. The Fund is managed according to FPA’s Contrarian Value Equity Strategy, which seeks to invest in companies that currently appear out of favor or undervalued but have a favorable outlook for growth in the portfolio manager’s estimation, over 5-10 years. The portfolio managers conduct deep research into the underlying financial condition and prospects of individual companies, and only select those whose securities are offered at a “substantial discount” to the portfolio managers’ estimation of the company’s worth or intrinsic value. TOP PERFORMANCE CONTRIBUTORS 1 Holcim, a building material (largely concrete, cement, and aggregates) company has performed well over the past year. In addition to strong operating performance, management has taken a number of steps to return value to shareholders and improve understanding of the company's underlying business strength, including share repurchases, increasing the dividend, and announcing plans to separate the company's North American business. Citigroup's shares have appreciated (along with other bank shares) from a profoundly depressed level of less than 50% of tangible book value (TBV) to a modestly depressed level of 70% TBV. TOP PERFORMANCE DETRACTORS 1 Charter has faced challenging operating conditions that have led to its share price weakness. Competitors have been overbuilding fixed wire assets. There has been concern regarding the sustainability of business derived from subsidized customers. And, the company's near-term capital spending budget has exceeded expectations. Its share price has also had greater volatility due to its relatively high leverage ratio. JDE Peet’s stock has declined over the past TTM, but earnings have been largely stable. However, a change in management, record-high coffee bean prices, and headwinds from the company’s Russia business have led investors to view the glass as half-empty. We are hopeful that new management will prove up to the task of making entrepreneurial and cost-efficient investments to reinvigorate growth and put JDE Peets in a position to benefit from its position as the world's second-largest consumer coffee company. 1 Past performance is no guarantee, nor is it indicative, of future results. |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | Fund Performance The following graph and chart compare the initial and subsequent account values at the end of each of the most recently completed 10 fiscal years of the Fund, or for the life of the Fund, if shorter. It assumes a $10,000 initial investment at the beginning of the first fiscal year in an appropriate, broad-based securities market index for the same period. GROWTH OF $10,000 |
| Average Annual Return [Table Text Block] | AVERAGE ANNUAL TOTAL RETURN 1 Year Since 1 FPA Global Equity ETF (FPAG) - NAV 31.24 % 9.23 % MSCI AC World Index (Net) 31.76 % 6.97 % 1 FPA Global Equity ETF commenced operations on December 16, 2021. |
| Performance Inception Date | Dec. 16, 2021 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Material Change Date | Apr. 26, 2024 |
| Updated Performance Information Location [Text Block] | Visit https://fpag.fpa.com/ |
| Net Assets | $ 153,425,491 |
| Holdings Count | Holding | 45 |
| Advisory Fees Paid, Amount | $ 142,062 |
| Investment Company Portfolio Turnover | 38% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics The following table outlines key fund statistics that you should pay attention to. Fund net assets $ Total number of portfolio holdings 45 Total advisory fees paid (net) $ Portfolio turnover rate as of the end of the reporting period 38 % |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. The Top Ten Holdings and Sector Allocation exclude short-term holdings, if any. The Top Ten Holdings table may not reflect the total exposure to an issuer. The Sector Allocation chart represents Common Stocks of the Fund. Top Ten Holdings Meta Platforms, Inc. - Class A 5.8 % Analog Devices, Inc. 5.5 % Holcim AG 5.2 % Comcast Corp. - Class A 5.1 % Citigroup, Inc. 4.8 % TE Connectivity PLC 4.7 % International Flavors & Fragrances, Inc. 4.7 % Alphabet, Inc. - Class A 4.0 % Wells Fargo & Co. 3.4 % Amazon.com, Inc. 3.4 % Asset Allocation Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Meta Platforms, Inc. - Class A 5.8 % Analog Devices, Inc. 5.5 % Holcim AG 5.2 % Comcast Corp. - Class A 5.1 % Citigroup, Inc. 4.8 % TE Connectivity PLC 4.7 % International Flavors & Fragrances, Inc. 4.7 % Alphabet, Inc. - Class A 4.0 % Wells Fargo & Co. 3.4 % Amazon.com, Inc. 3.4 % |
| Material Fund Change [Text Block] | Material Fund Changes Effective at the close of business day April 26, 2024, the Fund was reorganized from Northern Lights Fund Trust III into Investment Managers Series Trust III (the "Trust"). Effective December 1, 2024, First Pacific Advisors, LP (the "Adviser") has voluntarily agreed to waive all of its management fee and pay all of the Fund’s operating expenses (excluding any front-end or contingent deferred loads, brokerage fees and commissions, acquired fund fees and expenses, borrowing costs (such as interest and dividend expense on securities sold short), taxes, and extraordinary expenses, such as litigation expenses (which may include indemnification of Fund officers and Trustees, and contractual indemnification of Fund service providers (other than the Adviser))) from December 1, 2024, through January 31, 2025. The Adviser will not seek recoupment of any management fee it waives or Fund expenses it pays during such period pursuant to this voluntary agreement. Effective on or about December 6, 2024 (the “Effective Date”), Foreside Financial Group, LLC will complete its acquisition of UMB Distribution Services, LLC, the Fund’s distributor. This is a summary of certain changes to the Fund since October 1, 2023. For more complete information, you may review the Fund's prospectus, which is dated January 26, 2024, as amended April 30, 2024 at https://fpag.fpa.com/ |
| Material Fund Change Name [Text Block] | Effective at the close of business day April 26, 2024, the Fund was reorganized from Northern Lights Fund Trust III into Investment Managers Series Trust III (the "Trust"). |
| Material Fund Change Expenses [Text Block] | Effective December 1, 2024, First Pacific Advisors, LP (the "Adviser") has voluntarily agreed to waive all of its management fee and pay all of the Fund’s operating expenses (excluding any front-end or contingent deferred loads, brokerage fees and commissions, acquired fund fees and expenses, borrowing costs (such as interest and dividend expense on securities sold short), taxes, and extraordinary expenses, such as litigation expenses (which may include indemnification of Fund officers and Trustees, and contractual indemnification of Fund service providers (other than the Adviser))) from December 1, 2024, through January 31, 2025. The Adviser will not seek recoupment of any management fee it waives or Fund expenses it pays during such period pursuant to this voluntary agreement. |
| Updated Prospectus Web Address | https://fpag.fpa.com/ |
| Accountant Change Statement [Text Block] | Tait, Weller & Baker LLP was appointed to serve as the Trust's independent registered public accounting firm for the fiscal year ended September 30, 2024 upon the reorganization of the Fund. Previously, Deloitte & Touche LLP |
| Accountant Change Disagreements [Text Block] | Changes in and Disagreements with Accountants Tait, Weller & Baker LLP was appointed to serve as the Trust's independent registered public accounting firm for the fiscal year ended September 30, 2024 upon the reorganization of the Fund. Previously, Deloitte & Touche LLP |
| Shareholder Report, Line Graph (Details) - USD ($) | 12 Months Ended | 34 Months Ended | ||||
| Sep. 30, 2024 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Dec. 16, 2021 | ||
| C000247942 [Member] | ||||||
| Account Value [Line Items] | ||||||
| Line Graph and Table Measure Name | FPA Global Equity ETF (FPAG) - NAV | |||||
| Account Value | $ 12,792 | $ 12,792 | $ 9,747 | $ 7,508 | $ 10,000 | |
| Average Annual Return, Percent | 31.24% | 9.23% | [1] | |||
| MSCI AC World Index Net [Member] | ||||||
| Account Value [Line Items] | ||||||
| Line Graph and Table Measure Name | MSCI AC World Index (Net) | |||||
| Account Value | $ 12,066 | $ 12,066 | $ 9,158 | $ 7,581 | $ 10,000 | |
| Average Annual Return, Percent | 31.76% | 6.97% | [1] | |||
| [1]FPA Global Equity ETF commenced operations on December 16, 2021. | ||||||
| Shareholder Report, Holdings (Details) - C000247942 [Member] | Sep. 30, 2024 |
| Analog Devices Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.50% |
| Holcim AG [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| Comcast Corp Class A [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| Citigroup Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| TE Connectivity PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| International Flavors And Fragrances Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| Alphabet Inc Class A [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| Wells Fargo And Co [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| Amazon com Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| Meta Platforms Inc Class A [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.80% |
| Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 25.50% |
| Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.70% |
| Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.40% |
| Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.40% |
| Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.40% |
| Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| Common Stock [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 95.50% |
| Exchange Traded Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Other Assets in Excess of Liabilities [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
