| Shareholder Report | 6 Months Ended |
| Jun. 30, 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 | Jun. 30, 2024 |
| C000012470 | |
| Shareholder Report [Line Items] | |
| Fund Name | Polaris Global Value Fund |
| Trading Symbol | PGVFX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about the Polaris Global Value Fund for the period of January 1, 2024, to June 30, 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 Polaris Global Value Fund for the period of January 1, 2024, to June 30, 2024. You can find additional information about the Fund at https://polarisfunds.com/resources |
| Additional Information Phone Number | (888) 263-5594 |
| Additional Information Website | https://polarisfunds.com/resources</span>/" id="sjs-B18"><span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 13.3333px; font-weight: 400; grid-area: auto; line-height: 20px; margin: 0px; overflow: visible; text-align: justify;">https://polarisfunds.com/resources</span>/ |
| 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 Polaris Global Value Fund $50 0.99% |
| Expenses Paid, Amount | $ 50 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | How did the Fund perform in the last six months? The Fund had positive absolute returns in nine of 11 sectors; however, an underweight in a heated information technology (IT) sector weighed on results, as did lackluster results in communication services and real estate. Top contributors included financials and industrials, while the Fund outperformed the World Index in materials, consumer staples and utilities. Geographically, the Fund had double-digit gains from out-of-benchmark allocations in South Korea, China and Chile, while beating the World Index in Germany, Switzerland and Singapore. The Fund was underweight and underperformed in a heated U.S. market (artificial intelligence momentum drove U.S. averages), with Canada, Norway, Japan and Italy as other detractors. Financials contributed most, largely due to positive absolute performance in a heavily-overweight sector. Double-digit gains from Allison Transmission Holding, General Dynamics and two Japanese trading companies boosted industrial sector results. In IT, SK Hynix gained in excess of 50% for the semi-annual period, continuing to dominate in high-bandwidth memory (HBM), while noting good price momentum in traditional dynamic random-access memory (DRAM) and NAND markets. Energy transition applications, AI, and automation demand increasing copper resources amidst limited supply. As a result, copper prices have been on an upward trajectory since the end of 2023; Lundin Mining Corp. and Antofagasta PLC were direct beneficiaries. Detractors included two banks, Webster Financial Corp. and Toronto-Dominion Bank, the latter of which faced an anti-money-laundering investigation. Teleperformance declined on renewed concerns that generative AI will disrupt the French call center’s business. Fellow French company VINCI SA, the concessions and construction company, trended down 25%; we can ascertain no reason for the decline other than geopolitical risk in the country. OpenText Corp. declined on slow software implementation due to delays from customers assessing their use of AI. Guidance was lowered and quarterly earnings fell short of expectations. Top Contributors Top Detractors SK Hynix, Inc. Crocs, Inc. United Therapeutics Corp. Allison Transmission Holdings, Inc. Williams Cos., Inc. OpenText Corp. Magna International, Inc. Teleperformance SE CVS Health Corp. Sally Beauty Holdings, Inc. |
| 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 Polaris Global Value Fund MSCI World Index 06/30/14 $10,000 $10,000 09/30/14 $9,487 $9,784 12/31/14 $9,714 $9,883 03/31/15 $10,215 $10,112 06/30/15 $10,303 $10,143 09/30/15 $9,396 $9,286 12/31/15 $9,864 $9,797 03/31/16 $9,934 $9,763 06/30/16 $9,608 $9,861 09/30/16 $10,489 $10,341 12/31/16 $11,015 $10,533 03/31/17 $11,539 $11,204 06/30/17 $12,139 $11,655 09/30/17 $12,593 $12,219 12/31/17 $13,285 $12,892 03/31/18 $12,954 $12,727 06/30/18 $13,126 $12,948 09/30/18 $13,352 $13,592 12/31/18 $11,603 $11,769 03/31/19 $12,807 $13,238 06/30/19 $13,214 $13,767 09/30/19 $13,060 $13,841 12/31/19 $14,248 $15,025 03/31/20 $9,725 $11,862 06/30/20 $11,539 $14,159 09/30/20 $12,043 $15,281 12/31/20 $15,196 $17,415 03/31/21 $16,850 $18,272 06/30/21 $17,304 $19,687 09/30/21 $17,122 $19,685 12/31/21 $17,535 $21,214 03/31/22 $16,725 $20,121 06/30/22 $14,562 $16,864 09/30/22 $13,214 $15,821 12/31/22 $15,428 $17,366 03/31/23 $15,862 $18,708 06/30/23 $16,132 $19,986 09/30/23 $15,772 $19,294 12/31/23 $17,707 $21,496 03/31/24 $18,754 $23,405 06/30/24 $18,571 $24,021 |
| Average Annual Return [Table Text Block] | One Year Five Year Ten Year Polaris Global Value Fund 15.12% 7.04% 6.39% MSCI World Index 20.19% 11.78% 9.16% |
| 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 | $ 422,383,916 |
| Holdings Count | Holding | 94 |
| Advisory Fees Paid, Amount | $ 1,643,523 |
| InvestmentCompanyPortfolioTurnover | 8% |
| Additional Fund Statistics [Text Block] | Fund Statistics Total Net Assets $422,383,916 # of Portfolio Holdings 94 Portfolio Turnover Rate 8% Investment Advisory Fees (Net of fees waived)
$1,643,523 |
| Holdings [Text Block] | Country Weightings (% total investments)* Value Value United States 40.4% South Korea 8.0% Japan 7.8% France 6.7% Canada 6.6% United Kingdom 6.3% Germany 5.8% Switzerland 3.7% Norway 3.5% Ireland 2.9% Sweden 2.0% Italy 1.5% Puerto Rico 1.5% Netherlands 1.2% Singapore 1.2% Chile 0.7% Colombia 0.2% Russia 0.0% * excluding cash equivalents |
| Largest Holdings [Text Block] | Top Ten Holdings (% of investments)* SK Hynix, Inc. 2.24% Microsoft Corp. 1.81% United Therapeutics Corp. 1.75% Allison Transmission Holdings, Inc. 1.71% Williams Cos., Inc. 1.69% Crocs, Inc. 1.67% Muenchener Rueckversicherungs-Gesellschaft AG in Muenchen, Class R 1.62% General Dynamics Corp. 1.57% Linde PLC 1.52% Smurfit Kappa Group PLC 1.50% * excluding cash equivalents |
