| Shareholder Report | 6 Months Ended |
| Sep. 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 | Sep. 30, 2024 |
| C000012453 | |
| Shareholder Report [Line Items] | |
| Fund Name | Payson Total Return Fund |
| Trading Symbol | PBFDX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about the Payson Total Return Fund for the period of April 1, 2024, to September 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 Payson Total Return Fund for the period of April 1, 2024, to September 30, 2024. You can find additional information about the Fund at www.hmpayson.com/what-we-do/investment-management/total-return-fund/. You can also request this information by contacting us at (800) 805-8258. |
| Additional Information Phone Number | (800) 805-8258 |
| Additional Information Website | www.hmpayson.com/what-we-do/investment-management/total-return-fund/ |
| 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 Payson Total Return Fund $41 0.80% |
| Expenses Paid, Amount | $ 41 |
| Expense Ratio, Percent | 0.80% |
| Factors Affecting Performance [Text Block] | How did the Fund perform in the last six months? The Payson Total Return Fund (the Fund) advanced in the six-month period ending September 30, 2024, but trailed the S&P 500 Index. The gain in the market has been driven largely by a handful of large cap technology companies (most of which are involved in the emerging field of artificial intelligence), as well as by better-than-expected US economic growth and declining inflation. The Fund’s overweight in the Technology sector, in addition to an overweight in Industrials, were positive contributors, as was the Fund’s stock selection in Communication Services. Stock selection in Consumer Discretionary, Financials, and Industrials, were the largest negative contributors. |
| 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 Payson Total Return Fund S&P 500 ® 9/30/14 $10,000 $10,000 12/31/14 $10,257 $10,493 3/31/15 $10,246 $10,593 6/30/15 $10,494 $10,622 9/30/15 $9,448 $9,939 12/31/15 $9,775 $10,638 3/31/16 $9,842 $10,782 6/30/16 $9,894 $11,047 9/30/16 $10,491 $11,472 12/31/16 $10,785 $11,911 3/31/17 $11,556 $12,633 6/30/17 $11,796 $13,024 9/30/17 $12,496 $13,607 12/31/17 $13,127 $14,511 3/31/18 $13,335 $14,401 6/30/18 $13,730 $14,896 9/30/18 $14,904 $16,044 12/31/18 $12,892 $13,875 3/31/19 $14,645 $15,769 6/30/19 $15,149 $16,447 9/30/19 $15,354 $16,727 12/31/19 $16,975 $18,244 3/31/20 $13,843 $14,668 6/30/20 $17,146 $17,682 9/30/20 $18,544 $19,260 12/31/20 $20,456 $21,600 3/31/21 $22,339 $22,934 6/30/21 $23,882 $24,895 9/30/21 $23,856 $25,040 12/31/21 $26,787 $27,801 3/31/22 $25,651 $26,522 6/30/22 $22,121 $22,252 9/30/22 $20,955 $21,165 12/31/22 $22,873 $22,766 3/31/23 $23,646 $24,473 6/30/23 $25,728 $26,612 9/30/23 $25,528 $25,741 12/31/23 $28,158 $28,750 3/31/24 $31,488 $31,785 6/30/24 $32,462 $33,147 9/30/24 $33,393 $35,098 |
| Average Annual Return [Table Text Block] | One Year Five Year Ten Year Payson Total Return Fund 30.81% 16.81% 12.81% S&P 500 ® 36.35% 15.98% 13.38% |
| 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 | $ 291,661,618 |
| Holdings Count | Holding | 33 |
| Advisory Fees Paid, Amount | $ 828,694 |
| InvestmentCompanyPortfolioTurnover | 48% |
| Additional Fund Statistics [Text Block] | Fund Statistics Total Net Assets $291,661,618 # of Portfolio Holdings 33 Portfolio Turnover Rate 48% Investment Advisory Fees Paid
$828,694 |
| Holdings [Text Block] | Sector Weightings (% total investments)* Value Value Information Technology 47.8% Industrials 18.6% Financials 9.1% Health Care 8.9% Consumer Discretionary 8.9% Energy 4.3% Consumer Staples 2.4% * excluding exchange traded funds |
| Largest Holdings [Text Block] | Top Ten Holdings (% total net assets) SPDR Portfolio S&P 500 ETF 7.17% Broadcom, Inc. 7.16% Apple, Inc. 6.89% NVIDIA Corp. 5.81% Alphabet, Inc., Class A 5.63% Meta Platforms, Inc., Class A 5.26% Amazon.com, Inc. 4.81% L3Harris Technologies, Inc. 3.83% Microsoft Corp. 3.42% Visa, Inc., Class A 3.17% |
