| Shareholder Report | 12 Months Ended |
| Aug. 31, 2024 USD ($) Holding |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | FORUM FUNDS |
| Entity Central Index Key | 0000315774 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Aug. 31, 2024 |
| C000091784 | |
| Shareholder Report [Line Items] | |
| Fund Name | MAI Managed Volatility Fund |
| Class Name | Institutional |
| Trading Symbol | MAIPX |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the MAI Managed Volatility Fund for the period of September 1, 2023, to August 31, 2024. |
| Shareholder Report Annual or Semi-Annual | Annual Shareholder Report |
| Additional Information [Text Block] | This annual shareholder report contains important information about the MAI Managed Volatility Fund for the period of September 1, 2023, to August 31, 2024. You can find additional information about the Fund at http://www.maifunds.com/. You can also request this information by contacting us at (877) 414-7884. |
| Additional Information Phone Number | (877) 414-7884 |
| Additional Information Website | http://www.maifunds.com/ |
| Expenses [Text Block] | What were the Fund's costs for the last year? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Institutional Class $104 0.99% |
| Expenses Paid, Amount | $ 104 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | How did the Fund perform in the last year? Over the year ending August 31, 2024, the Fund's Institutional Class (MAIPX) returned 9.66% Over the same period, the S&P 500 ® The Fund’s targeted exposure of 45-55% to a diversified equity portfolio helped the Fund advance but could not keep pace with a market driven by the sharp rise of a few companies. Markets priced risk significantly below the long-term average levels for most of the year, leading the Fund to be cautious with its option writing activities. In August, markets marked one of the largest volatility shifts in the history of the CBOE Volatility Index (“VIX”) 1 The Fund’s limited equity exposure coupled with its risk managed approach to option writing limited its participation in the market’s three sharp pullbacks and rallies. The Fund advanced with less volatility and successfully navigated the August volatility spike. Net returns were above the Fund’s historical average. We believe the Fund’s ability to generate returns through non-directional investments (Interest, Dividends, Option Writing) aids in its ability to generate returns commensurate with investor expectations. 1 |
| 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 Institutional Class S&P 500 ® 08/31/14 $50,000 $50,000 11/30/14 $49,832 $51,861 02/28/15 $50,568 $53,061 05/31/15 $51,048 $53,401 08/31/15 $49,001 $50,239 11/30/15 $50,220 $53,287 02/29/16 $48,735 $49,777 05/31/16 $50,590 $54,318 08/31/16 $51,771 $56,545 11/30/16 $51,900 $57,581 02/28/17 $53,594 $62,208 05/31/17 $54,119 $63,806 08/31/17 $54,980 $65,725 11/30/17 $56,670 $70,752 02/28/18 $56,849 $72,846 05/31/18 $57,614 $72,984 08/31/18 $59,940 $78,648 11/30/18 $59,290 $75,191 02/28/19 $59,216 $76,255 05/31/19 $59,596 $75,745 08/31/19 $61,935 $80,945 11/30/19 $63,972 $87,304 02/29/20 $60,594 $82,503 05/31/20 $60,839 $85,468 08/31/20 $63,434 $98,702 11/30/20 $66,351 $102,544 02/28/21 $67,795 $108,318 05/31/21 $71,177 $119,928 08/31/21 $73,026 $129,463 11/30/21 $74,294 $131,175 02/28/22 $73,819 $126,071 05/31/22 $72,656 $119,569 08/31/22 $71,936 $114,928 11/30/22 $74,067 $119,094 02/28/23 $73,968 $116,374 05/31/23 $76,372 $123,062 08/31/23 $77,895 $133,252 11/30/23 $79,860 $135,576 02/29/24 $81,911 $151,813 05/31/24 $83,152 $157,749 08/31/24 $85,422 $169,411 |
| Average Annual Return [Table Text Block] | One Year Five Year Ten Year Institutional Class 9.66% 6.64% 5.50% S&P 500 ® 27.14% 15.92% 12.98% |
| 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] | |
| AssetsNet | $ 244,962,792 |
| Holdings Count | Holding | 84 |
| Advisory Fees Paid, Amount | $ 1,676,896 |
| InvestmentCompanyPortfolioTurnover | 6% |
| Additional Fund Statistics [Text Block] | Fund Statistics Total Net Assets $244,962,792 # of Portfolio Holdings 84 Portfolio Turnover Rate 6% Investment Advisory Fees (Net of fees waived)
$1,676,896 |
| Holdings [Text Block] | Sector Weightings (% of investments)* Value Value Information Technology 32.0% Financials 15.0% Health Care 12.9% Communication Services 10.5% Consumer Discretionary 8.1% Consumer Staples 6.6% Industrials 6.2% Energy 4.1% Utilities 2.6% Real Estate 1.5% Materials 0.5% * excluding fixed income securities and cash equivalents |
| Largest Holdings [Text Block] | Top Ten Holdings (% of investments)* Apple, Inc. 8.05% Microsoft Corp. 7.08% Alphabet, Inc., Class A 4.03% Amazon.com, Inc. 3.43% UnitedHealth Group, Inc. 3.40% Visa, Inc., Class A 3.39% Broadcom, Inc. 3.34% Meta Platforms, Inc., Class A 3.27% The Home Depot, Inc. 3.17% Oracle Corp. 2.98% * excluding fixed income securities and cash equivalents |
| C000091785 | |
| Shareholder Report [Line Items] | |
| Fund Name | MAI Managed Volatility Fund |
| Class Name | Investor |
| Trading Symbol | DIVPX |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about the MAI Managed Volatility Fund for the period of September 1, 2023, to August 31, 2024. |
| Shareholder Report Annual or Semi-Annual | Annual Shareholder Report |
| Additional Information [Text Block] | This annual shareholder report contains important information about the MAI Managed Volatility Fund for the period of September 1, 2023, to August 31, 2024. You can find additional information about the Fund at http://www.maifunds.com/. You can also request this information by contacting us at (877) 414-7884. |
| Additional Information Phone Number | (877) 414-7884 |
| Additional Information Website | http://www.maifunds.com/ |
| Expenses [Text Block] | What were the Fund's costs for the last year? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Investor Class $130 1.24% |
| Expenses Paid, Amount | $ 130 |
| Expense Ratio, Percent | 1.24% |
| Factors Affecting Performance [Text Block] | How did the Fund perform in the last year? Over the year ending August 31, 2024, the Fund's Investor Class (DIVPX) returned 9.40%. Over the same period, the S&P 500 ® The Fund’s targeted exposure of 45-55% to a diversified equity portfolio helped the Fund advance but could not keep pace with a market driven by the sharp rise of a few companies. Markets priced risk significantly below the long-term average levels for most of the year, leading the Fund to be cautious with its option writing activities. In August, markets marked one of the largest volatility shifts in the history of the CBOE Volatility Index ("VIX") 1 The Fund’s limited equity exposure coupled with its risk managed approach to option writing limited its participation in the market’s three sharp pullbacks and rallies. The Fund advanced with less volatility and successfully navigated the August volatility spike. Net returns were above the Fund’s historical average. We believe the Fund’s ability to generate returns through non-directional investments (Interest, Dividends, Option Writing) aids in its ability to generate returns commensurate with investor expectations. 1 |
| 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 Investor Class S&P 500 ® 08/31/14 $10,000 $10,000 11/30/14 $9,957 $10,372 02/28/15 $10,097 $10,612 05/31/15 $10,189 $10,680 08/31/15 $9,767 $10,048 11/30/15 $10,006 $10,657 02/29/16 $9,705 $9,955 05/31/16 $10,070 $10,864 08/31/16 $10,300 $11,309 11/30/16 $10,320 $11,516 02/28/17 $10,647 $12,442 05/31/17 $10,753 $12,761 08/31/17 $10,907 $13,145 11/30/17 $11,245 $14,150 02/28/18 $11,270 $14,569 05/31/18 $11,408 $14,597 08/31/18 $11,858 $15,730 11/30/18 $11,731 $15,038 02/28/19 $11,702 $15,251 05/31/19 $11,766 $15,149 08/31/19 $12,222 $16,189 11/30/19 $12,619 $17,461 02/29/20 $11,941 $16,501 05/31/20 $11,992 $17,094 08/31/20 $12,494 $19,740 11/30/20 $13,056 $20,509 02/28/21 $13,327 $21,664 05/31/21 $13,990 $23,986 08/31/21 $14,342 $25,893 11/30/21 $14,583 $26,235 02/28/22 $14,482 $25,214 05/31/22 $14,241 $23,914 08/31/22 $14,091 $22,986 11/30/22 $14,502 $23,819 02/28/23 $14,479 $23,275 05/31/23 $14,932 $24,612 08/31/23 $15,222 $26,650 11/30/23 $15,588 $27,115 02/29/24 $15,989 $30,363 05/31/24 $16,218 $31,550 08/31/24 $16,652 $33,882 |
| Average Annual Return [Table Text Block] | One Year Five Year Ten Year Investor Class 9.40% 6.38% 5.23% S&P 500 ® 27.14% 15.92% 12.98% |
| 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 | $ 244,962,792 |
| Holdings Count | Holding | 84 |
| Advisory Fees Paid, Amount | $ 1,676,896 |
| InvestmentCompanyPortfolioTurnover | 6% |
| Additional Fund Statistics [Text Block] | Fund Statistics Total Net Assets $244,962,792 # of Portfolio Holdings 84 Portfolio Turnover Rate 6% Investment Advisory Fees (Net of fees waived)
$1,676,896 |
| Holdings [Text Block] | Sector Weightings (% of investments)* Value Value Information Technology 32.0% Financials 15.0% Health Care 12.9% Communication Services 10.5% Consumer Discretionary 8.1% Consumer Staples 6.6% Industrials 6.2% Energy 4.1% Utilities 2.6% Real Estate 1.5% Materials 0.5% * excluding fixed income securities and cash equivalents |
| Largest Holdings [Text Block] | Top Ten Holdings (% of investments)* Apple, Inc. 8.05% Microsoft Corp. 7.08% Alphabet, Inc., Class A 4.03% Amazon.com, Inc. 3.43% UnitedHealth Group, Inc. 3.40% Visa, Inc., Class A 3.39% Broadcom, Inc. 3.34% Meta Platforms, Inc., Class A 3.27% The Home Depot, Inc. 3.17% Oracle Corp. 2.98% * excluding fixed income securities and cash equivalents |
