| Form N-CSR Cover | 6 Months Ended |
| Oct. 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | FORUM FUNDS |
| Entity Central Index Key | 0000315774 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Oct. 31, 2024 |
| Shareholder Report | 6 Months Ended |
| Oct. 31, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | FORUM FUNDS |
| Entity Central Index Key | 0000315774 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Oct. 31, 2024 |
| C000126338 | |
| Shareholder Report [Line Items] | |
| Fund Name | Monongahela All Cap Value Fund |
| Trading Symbol | MCMVX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about the Monongahela All Cap Value Fund for the period of May 1, 2024, to October 31, 2024. |
| Shareholder Report Annual or Semi-Annual | Semi-Annual Shareholder Report |
| Additional Information [Text Block] | This semi-annual shareholder report contains important information about the Monongahela All Cap Value Fund for the period of May 1, 2024, to October 31, 2024. You can find additional information about the Fund at www.Moncapfund.com. You can also request this information by contacting us at (855) 392-9331. |
| Additional Information Phone Number | (855) 392-9331 |
| Additional Information Website | www.Moncapfund.com |
| Expenses [Text Block] | What were the Fund's costs for the last six months? (based on a hypothetical $10,000 investment) Fund Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Monongahela All Cap Value Fund $44 0.85% |
| Expenses Paid, Amount | $ 44 |
| Expense Ratio, Percent | 0.85% |
| Factors Affecting Performance [Text Block] | How did the Fund perform in the last six months? We offer this semi-annual report for the Monongahela All Cap Value Fund (the “Fund”) for the period from May 1, 2024 to October 31, 2024 (the “period”). During the period the Fund was up 8.01%, the S&P 500 Index (an index of the 500 largest publicly traded companies in the US weighted by market capitalization) was up 14.08% and the Russell 2000 Value Index (an Index that tracks the performance of small capitalization value companies) was up 11.59%. The Fund underperformed the S&P 500 Index and the Russell 2000 Value Index for the period primarily due to sector weighting. Compared to the S&P 500 Index, the Fund was underweighted in Information Technology and Financials sectors and overweighted in Consumer Staples and Industrials sectors. Compared to the Russell 2000 Value Index, the Fund was significantly underweighted in the Financial sector (6.9% vs. 28.14%) and overweighted in the Consumer Staples Sector (17.1% vs 2.06%). With our bottom-up approach to security analysis, we try to identify equities trading below intrinsic value and priced with a margin of safety. In that view, we have increased our exposure to Consumer Staples, adding The Estee Lauder Cos., Inc, The Hershey Co. and increasing our position in Lamb Weston Holdings Inc. and WK Kellogg Co. We have added Coherent Corp. to our Information Technology sector. Leadership is a key metric for us and we were pleased with the appointment of James Anderson as the new CEO for Coherent Corp. on June 3rd, 2024. Our current allocation reflects our perception of value going forward, mindful of risk. |
| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | Date Monongahela All Cap Value Fund S&P 500 ® Russell 2000 ® 10/31/14 $10,000 $10,000 $10,000 01/31/15 $10,008 $9,936 $9,800 04/30/15 $10,326 $10,440 $10,205 07/31/15 $10,220 $10,586 $10,019 10/31/15 $9,858 $10,520 $9,712 01/31/16 $9,331 $9,869 $8,826 04/30/16 $10,264 $10,566 $9,827 07/31/16 $10,848 $11,181 $10,579 10/31/16 $10,955 $10,994 $10,568 01/31/17 $12,158 $11,847 $12,376 04/30/17 $12,643 $12,459 $12,498 07/31/17 $12,955 $12,974 $12,612 10/31/17 $13,550 $13,593 $13,190 01/31/18 $14,778 $14,976 $13,608 04/30/18 $13,826 $14,112 $13,314 07/31/18 $14,728 $15,081 $14,424 10/31/18 $13,867 $14,591 $13,112 01/31/19 $14,457 $14,629 $12,994 04/30/19 $15,170 $16,016 $13,606 07/31/19 $15,138 $16,286 $13,311 10/31/19 $15,668 $16,681 $13,534 01/31/20 $16,142 $17,802 $13,563 04/30/20 $14,069 $16,154 $10,361 07/31/20 $15,696 $18,233 $11,194 10/31/20 $16,120 $18,301 $11,650 01/31/21 $19,562 $20,872 $15,789 04/30/21 $22,079 $23,582 $18,543 07/31/21 $22,452 $24,878 $18,324 10/31/21 $22,226 $26,155 $19,141 01/31/22 $22,587 $25,734 $18,119 04/30/22 $21,698 $23,632 $17,322 07/31/22 $21,747 $23,724 $17,451 10/31/22 $20,798 $22,334 $17,087 01/31/23 $22,391 $23,619 $18,024 04/30/23 $21,716 $24,262 $15,938 07/31/23 $23,079 $26,812 $18,139 10/31/23 $20,811 $24,599 $15,391 01/31/24 $23,695 $28,536 $18,007 04/30/24 $25,301 $29,760 $18,174 07/31/24 $27,039 $32,750 $20,983 10/31/24 $27,329 $33,950 $20,280 |
| Average Annual Return [Table Text Block] | One Year Five Year Ten Year Monongahela All Cap Value Fund 31.32% 11.77% 10.58% S&P 500 ® 38.02% 15.27% 13.00% Russell 2000 ® 31.77% 8.42% 7.33% |
| 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. |
| Performance Table Market Index Changed [Text Block] | |
| Updated Performance Information Location [Text Block] | |
| AssetsNet | $ 33,716,277 |
| Holdings Count | Holding | 56 |
| Advisory Fees Paid, Amount | $ 27,263 |
| InvestmentCompanyPortfolioTurnover | 7% |
| Additional Fund Statistics [Text Block] | Fund Statistics Total Net Assets $33,716,277 # of Portfolio Holdings 56 Portfolio Turnover Rate 7% Investment Advisory Fees (Net of fees waived) $27,263 |
| Holdings [Text Block] | Sector Weightings (% total investments) Value Value Money Market Fund 1.3% Utilities 1.0% Materials 2.8% Energy 4.3% Financials 6.9% Consumer Discretionary 14.0% Information Technology 14.1% Health Care 15.4% Consumer Staples 17.1% Industrials 23.1% |
| Largest Holdings [Text Block] | Top Ten Holdings (% of total investments) Curtiss-Wright Corp. 4.09% Williams-Sonoma, Inc. 3.98% Westinghouse Air Brake Technologies Corp. 3.63% Revvity, Inc. 3.61% MetLife, Inc. 3.38% Rockwell Automation, Inc. 3.36% Merck & Co., Inc. 3.19% Hubbell, Inc. 3.17% Hologic, Inc. 3.12% Lindsay Corp. 3.11% |
| Shareholder Report, Line Graph (Details) - USD ($) | 6 Months Ended | ||||||||||||||||||||||||||||||||||||||||
| Oct. 31, 2024 | Jul. 31, 2024 | Apr. 30, 2024 | Jan. 31, 2024 | Oct. 31, 2023 | Jul. 31, 2023 | Apr. 30, 2023 | Jan. 31, 2023 | Oct. 31, 2022 | Jul. 31, 2022 | Apr. 30, 2022 | Jan. 31, 2022 | Oct. 31, 2021 | Jul. 31, 2021 | Apr. 30, 2021 | Jan. 31, 2021 | Oct. 31, 2020 | Jul. 31, 2020 | Apr. 30, 2020 | Jan. 31, 2020 | Oct. 31, 2019 | Jul. 31, 2019 | Apr. 30, 2019 | Jan. 31, 2019 | Oct. 31, 2018 | Jul. 31, 2018 | Apr. 30, 2018 | Jan. 31, 2018 | Oct. 31, 2017 | Jul. 31, 2017 | Apr. 30, 2017 | Jan. 31, 2017 | Oct. 31, 2016 | Jul. 31, 2016 | Apr. 30, 2016 | Jan. 31, 2016 | Oct. 31, 2015 | Jul. 31, 2015 | Apr. 30, 2015 | Jan. 31, 2015 | Oct. 31, 2014 | |
| C000126338 | |||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||
| Line Graph and Table Measure Name | Monongahela All Cap Value Fund | ||||||||||||||||||||||||||||||||||||||||
| S&P 500® Index | |||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||
| Line Graph and Table Measure Name | ®</sup> Index" id="sjs-B8">S&P 500<sup style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 700; grid-area: auto; line-height: 0px; margin: 0px; overflow: visible; position: relative; text-align: center;">®</sup> Index | ||||||||||||||||||||||||||||||||||||||||
| Account Value | $ 33,950 | $ 32,750 | $ 29,760 | $ 28,536 | $ 24,599 | $ 26,812 | $ 24,262 | $ 23,619 | $ 22,334 | $ 23,724 | $ 23,632 | $ 25,734 | $ 26,155 | $ 24,878 | $ 23,582 | $ 20,872 | $ 18,301 | $ 18,233 | $ 16,154 | $ 17,802 | $ 16,681 | $ 16,286 | $ 16,016 | $ 14,629 | $ 14,591 | $ 15,081 | $ 14,112 | $ 14,976 | $ 13,593 | $ 12,974 | $ 12,459 | $ 11,847 | $ 10,994 | $ 11,181 | $ 10,566 | $ 9,869 | $ 10,520 | $ 10,586 | $ 10,440 | $ 9,936 | $ 10,000 |
| Russell 2000 Value Index | |||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||
| Line Graph and Table Measure Name | ®</sup> Value Index" id="sjs-B12">Russell 2000<sup style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 700; grid-area: auto; line-height: 0px; margin: 0px; overflow: visible; position: relative; text-align: center;">®</sup> Value Index | ||||||||||||||||||||||||||||||||||||||||
| Account Value | $ 20,280 | $ 20,983 | $ 18,174 | $ 18,007 | $ 15,391 | $ 18,139 | $ 15,938 | $ 18,024 | $ 17,087 | $ 17,451 | $ 17,322 | $ 18,119 | $ 19,141 | $ 18,324 | $ 18,543 | $ 15,789 | $ 11,650 | $ 11,194 | $ 10,361 | $ 13,563 | $ 13,534 | $ 13,311 | $ 13,606 | $ 12,994 | $ 13,112 | $ 14,424 | $ 13,314 | $ 13,608 | $ 13,190 | $ 12,612 | $ 12,498 | $ 12,376 | $ 10,568 | $ 10,579 | $ 9,827 | $ 8,826 | $ 9,712 | $ 10,019 | $ 10,205 | $ 9,800 | $ 10,000 |
| Shareholder Report, Average Annual Return (Details) | 6 Months Ended | 12 Months Ended | 60 Months Ended | 120 Months Ended |
| Oct. 31, 2024 | Oct. 31, 2024 | Oct. 31, 2024 | Oct. 31, 2024 | |
| C000126338 | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | Monongahela All Cap Value Fund | |||
| Without Sales Load [Member] | C000126338 | ||||
| Average Annual Return [Line Items] | ||||
| Average Annual Return, Percent | 31.32% | 11.77% | 10.58% | |
| S&P 500® Index | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | ®</sup> Index" id="sjs-B11">S&P 500<sup style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 700; grid-area: auto; line-height: 0px; margin: 0px; overflow: visible; position: relative; text-align: center;">®</sup> Index | |||
| Average Annual Return, Percent | 38.02% | 15.27% | 13% | |
| Russell 2000 Value Index | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | ®</sup> Value Index" id="sjs-B15">Russell 2000<sup style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 700; grid-area: auto; line-height: 0px; margin: 0px; overflow: visible; position: relative; text-align: center;">®</sup> Value Index | |||
| Average Annual Return, Percent | 31.77% | 8.42% | 7.33% |
| Shareholder Report, Holdings (Details) - C000126338 | Oct. 31, 2024 |
| Curtiss-Wright Corp.None_231561101 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.09% |
| Williams-Sonoma, Inc.None_969904101 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.98% |
| Westinghouse Air Brake Technologies Corp.None_929740108 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.63% |
| Revvity, Inc.None_714046109 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.61% |
| MetLife, Inc.None_59156R108 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.38% |
| Rockwell Automation, Inc.None_773903109 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.36% |
| Merck & Co., Inc.None_58933Y105 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.19% |
| Hubbell, Inc.None_443510607 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.17% |
| Hologic, Inc.None_436440101 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.12% |
| Lindsay Corp.None_535555106 | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.11% |
| Money Market Fund | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| Utilities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Materials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| Energy | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| Financials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.90% |
| Consumer Discretionary | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14% |
| Information Technology | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.10% |
| Health Care | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.40% |
| Consumer Staples | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.10% |
| Industrials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.10% |
