| 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 |
| C000012485 | |
| Shareholder Report [Line Items] | |
| Fund Name | Lisanti Small Cap Growth Fund |
| Trading Symbol | ASCGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about the Lisanti Small Cap Growth 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 Lisanti Small Cap Growth Fund for the period of January 1, 2024, to June 30, 2024. You can find additional information about the Fund at https://lisantismallcap.com/investing-in-the-fund |
| Additional Information Phone Number | (800) 441-7031 |
| Additional Information Website | https://lisantismallcap.com/investing-in-the-fund</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: left;">https://lisantismallcap.com/investing-in-the-fund</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 Lisanti Small Cap Growth Fund $72 1.34% |
| Expenses Paid, Amount | $ 72 |
| Expense Ratio, Percent | 1.34% |
| Factors Affecting Performance [Text Block] | How did the Fund perform in the last six months? Performance of the Fund in the first half of 2024 was driven by individual stock selection. The Fund’s investment process focuses on companies that have individual, idiosyncratic drivers of growth and are showing or on the path to show strong operating leverage. The Consumer Discretionary, Healthcare and Industrials sectors were the greatest contributors to outperformance, while Financials and Communications Services detracted modestly from performance. The focus in Consumer Discretionary was on companies that have transformed their business models to adapt to the new environment, and that offer a very strong value proposition to a more discerning and disciplined consumer, such as Modine Manufacturing, Abercrombie & Fitch and Freshpet. In Healthcare, the Fund benefited from companies with very strong growth profiles that offer innovative therapies and/or devices to solve significant medical challenges, such as Viking Therapeutics, TransMedics Group, and PROCEPT BioRobotics. In Industrials, the team focused on companies that solved critical issues, such as FTAI Aviation, which provides parts to the aerospace industry. |
| 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 Lisanti Small Cap Growth Fund Russell 2000 ® Russell 2000 Growth Index 06/30/14 $10,000 $10,000 $10,000 09/30/14 $9,507 $9,264 $9,387 12/31/14 $10,473 $10,165 $10,331 03/31/15 $11,060 $10,604 $11,016 06/30/15 $11,859 $10,649 $11,234 09/30/15 $10,674 $9,379 $9,767 12/31/15 $10,454 $9,717 $10,189 03/31/16 $9,535 $9,569 $9,711 06/30/16 $9,623 $9,932 $10,026 09/30/16 $10,713 $10,830 $10,951 12/31/16 $11,219 $11,787 $11,342 03/31/17 $11,866 $12,078 $11,948 06/30/17 $12,656 $12,375 $12,473 09/30/17 $13,441 $13,077 $13,248 12/31/17 $14,336 $13,513 $13,856 03/31/18 $14,824 $13,502 $14,174 06/30/18 $16,280 $14,549 $15,200 09/30/18 $18,239 $15,069 $16,039 12/31/18 $14,064 $12,025 $12,566 03/31/19 $16,534 $13,779 $14,721 06/30/19 $17,567 $14,067 $15,125 09/30/19 $16,510 $13,730 $14,494 12/31/19 $17,669 $15,094 $16,145 03/31/20 $13,787 $10,473 $11,986 06/30/20 $19,155 $13,135 $15,651 09/30/20 $21,071 $13,783 $16,772 12/31/20 $27,007 $18,107 $21,737 03/31/21 $28,507 $20,407 $22,797 06/30/21 $29,824 $21,283 $23,690 09/30/21 $29,022 $20,355 $22,351 12/31/21 $29,892 $20,791 $22,353 03/31/22 $25,584 $19,226 $19,530 06/30/22 $19,087 $15,920 $15,770 09/30/22 $19,168 $15,572 $15,808 12/31/22 $18,720 $16,542 $16,461 03/31/23 $19,618 $16,995 $17,461 06/30/23 $20,174 $17,879 $18,692 09/30/23 $17,952 $16,962 $17,324 12/31/23 $19,536 $19,342 $19,533 03/31/24 $22,206 $20,344 $21,014 06/30/24 $22,856 $19,677 $20,400 |
| Average Annual Return [Table Text Block] | One Year Five Year Ten Year Lisanti Small Cap Growth Fund 13.30% 5.41% 8.62% Russell 2000 ® 10.06% 6.94% 7.00% Russell 2000 Growth Index 9.14% 6.17% 7.39% |
| 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] | Effective May 1, 2024, the Fund changed its primary benchmark from the Russell 2000 Growth Index to the Russell 2000 Index due to regulatory requirements. The Fund retained the Russell 2000 Growth Index as a secondary benchmark because the Russell 2000 Growth Index more closely aligns with the Fund’s investment strategies and investment restrictions. |
| Prior Market Index Comparison [Text Block] | The Fund retained the Russell 2000 Growth Index as a secondary benchmark |
| Updated Performance Information Location [Text Block] | |
| AssetsNet | $ 26,328,534 |
| Holdings Count | Holding | 88 |
| Advisory Fees Paid, Amount | $ 34,675 |
| InvestmentCompanyPortfolioTurnover | 101% |
| Additional Fund Statistics [Text Block] | Fund Statistics Total Net Assets $26,328,534 # of Portfolio Holdings 88 Portfolio Turnover Rate 101% Investment Advisory Fees (Net of fees waived)
$34,675 |
| Holdings [Text Block] | Sector Weightings (% total investments)* Value Value Industrials 27.3% Information Technology 25.0% Health-Care 20.6% Consumer Discretionary 14.8% Consumer Staples 4.2% Energy 3.7% Materials 2.0% Financials 1.2% Communication Services 1.2% * excluding cash equivalents |
| Largest Holdings [Text Block] | Top Ten Holdings (% of investments)* FTAI Aviation, Ltd. 2.70% Q2 Holdings, Inc. 2.43% Freshpet, Inc. 2.37% PROCEPT BioRobotics Corp. 2.25% Ollie's Bargain Outlet Holdings, Inc. 2.19% Federal Signal Corp. 1.98% TransMedics Group, Inc. 1.90% FormFactor, Inc. 1.86% Credo Technology Group Holding, Ltd. 1.81% SPX Technologies, Inc. 1.81% * excluding cash equivalents |
| Updated Prospectus Web Address | https://lisantismallcap.com/investing-in-the-fund</span>" id="sjs-B37"><span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left;">https://lisantismallcap.com/investing-in-the-fund</span> |
