| Form N-CSR Cover | 6 Months Ended |
| Jun. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Legg Mason Global Asset Management Trust |
| Entity Central Index Key | 0001474103 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Shareholder Report | 6 Months Ended | |
| Jun. 30, 2024 USD ($) $ / shares | ||
| Shareholder Report [Line Items] | ||
| Document Type | N-CSRS | |
| Amendment Flag | false | |
| Registrant Name | Legg Mason Global Asset Management Trust | |
| Entity Central Index Key | 0001474103 | |
| Entity Investment Company Type | N-1A | |
| Document Period End Date | Jun. 30, 2024 | |
| Class A | ||
| Shareholder Report [Line Items] | ||
| Fund Name | BrandywineGLOBAL - Small Cap Value Fund | |
| Class Name | Class A | |
| Trading Symbol | LEGDX | |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about BrandywineGLOBAL - Small Cap Value Fund for the period January 1, 2024, to June 30, 2024. | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents . You can also request this information by contacting us at 877-6LM-FUND/656-3863 . | |
| Additional Information Phone Number | 877-6LM-FUND/656-3863 | |
| Additional Information Website | https://www.franklintempleton.com/regulatory-fund-documents | |
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (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 * , † Class A $61 1.25% | [1],[2] |
| Expenses Paid, Amount | $ 61 | |
| Expense Ratio, Percent | 1.25% | |
| Net Assets | $ 19,476,181 | |
| Holdings Count | $ / shares | 65 | [3] |
| Investment Company Portfolio Turnover | 25% | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of June 30, 2024) Total Net Assets $19,476,181 Total Number of Portfolio Holdings * 65 Portfolio Turnover Rate 25% | [3] |
| Holdings [Text Block] | ||
| Updated Prospectus Web Address | https://www.franklintempleton.com/regulatory-fund-documents | |
| Class C | ||
| Shareholder Report [Line Items] | ||
| Fund Name | BrandywineGLOBAL - Small Cap Value Fund | |
| Class Name | Class C | |
| Trading Symbol | LEGEX | |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about BrandywineGLOBAL - Small Cap Value Fund for the period January 1, 2024, to June 30, 2024. | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents . You can also request this information by contacting us at 877-6LM-FUND/656-3863 . | |
| Additional Information Phone Number | 877-6LM-FUND/656-3863 | |
| Additional Information Website | https://www.franklintempleton.com/regulatory-fund-documents | |
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (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 * , † Class C $91 1.87% | [4],[5] |
| Expenses Paid, Amount | $ 91 | |
| Expense Ratio, Percent | 1.87% | |
| Net Assets | $ 19,476,181 | |
| Holdings Count | $ / shares | 65 | [6] |
| Investment Company Portfolio Turnover | 25% | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of June 30, 2024) Total Net Assets $19,476,181 Total Number of Portfolio Holdings * 65 Portfolio Turnover Rate 25% | [6] |
| Holdings [Text Block] | ||
| Updated Prospectus Web Address | https://www.franklintempleton.com/regulatory-fund-documents | |
| Class R | ||
| Shareholder Report [Line Items] | ||
| Fund Name | BrandywineGLOBAL - Small Cap Value Fund | |
| Class Name | Class R | |
| Trading Symbol | LEGHX | |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about BrandywineGLOBAL - Small Cap Value Fund for the period January 1, 2024, to June 30, 2024. | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents . You can also request this information by contacting us at 877-6LM-FUND/656-3863 . | |
| Additional Information Phone Number | 877-6LM-FUND/656-3863 | |
| Additional Information Website | https://www.franklintempleton.com/regulatory-fund-documents | |
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (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 * , † Class R $72 1.48% | [7],[8] |
| Expenses Paid, Amount | $ 72 | |
| Expense Ratio, Percent | 1.48% | |
| Net Assets | $ 19,476,181 | |
| Holdings Count | $ / shares | 65 | [9] |
| Investment Company Portfolio Turnover | 25% | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of June 30, 2024) Total Net Assets $19,476,181 Total Number of Portfolio Holdings * 65 Portfolio Turnover Rate 25% | [9] |
| Holdings [Text Block] | ||
| Updated Prospectus Web Address | https://www.franklintempleton.com/regulatory-fund-documents | |
| Class I | ||
| Shareholder Report [Line Items] | ||
| Fund Name | BrandywineGLOBAL - Small Cap Value Fund | |
| Class Name | Class I | |
| Trading Symbol | LEGFX | |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about BrandywineGLOBAL - Small Cap Value Fund for the period January 1, 2024, to June 30, 2024. | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents . You can also request this information by contacting us at 877-6LM-FUND/656-3863 . | |
| Additional Information Phone Number | 877-6LM-FUND/656-3863 | |
| Additional Information Website | https://www.franklintempleton.com/regulatory-fund-documents | |
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (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 * , † Class I $49 1.00% | [10],[11] |
| Expenses Paid, Amount | $ 49 | |
| Expense Ratio, Percent | 1% | |
| Net Assets | $ 19,476,181 | |
| Holdings Count | $ / shares | 65 | [12] |
| Investment Company Portfolio Turnover | 25% | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of June 30, 2024) Total Net Assets $19,476,181 Total Number of Portfolio Holdings * 65 Portfolio Turnover Rate 25% | [12] |
| Holdings [Text Block] | ||
| Updated Prospectus Web Address | https://www.franklintempleton.com/regulatory-fund-documents | |
| Class IS | ||
| Shareholder Report [Line Items] | ||
| Fund Name | BrandywineGLOBAL - Small Cap Value Fund | |
| Class Name | Class IS | |
| Trading Symbol | LEGGX | |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about BrandywineGLOBAL - Small Cap Value Fund for the period January 1, 2024, to June 30, 2024. | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents . You can also request this information by contacting us at 877-6LM-FUND/656-3863 . | |
| Additional Information Phone Number | 877-6LM-FUND/656-3863 | |
| Additional Information Website | https://www.franklintempleton.com/regulatory-fund-documents | |
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (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 * , † Class IS $44 0.90% | [13],[14] |
| Expenses Paid, Amount | $ 44 | |
| Expense Ratio, Percent | 0.90% | |
| Net Assets | $ 19,476,181 | |
| Holdings Count | $ / shares | 65 | [15] |
| Investment Company Portfolio Turnover | 25% | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of June 30, 2024) Total Net Assets $19,476,181 Total Number of Portfolio Holdings * 65 Portfolio Turnover Rate 25% | [15] |
| Holdings [Text Block] | ||
| Updated Prospectus Web Address | https://www.franklintempleton.com/regulatory-fund-documents | |
| [1] * Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher. † Annualized. * Does not include derivatives, except purchased options, if any. * Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher. † Annualized. * Does not include derivatives, except purchased options, if any. * Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher. † Annualized. * Does not include derivatives, except purchased options, if any. * Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher. † Annualized. * Does not include derivatives, except purchased options, if any. * Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher. † Annualized. * Does not include derivatives, except purchased options, if any. | ||
| Shareholder Report, Holdings (Details) | Jun. 30, 2024 |
| Class A | Financials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 26.50% |
| Class A | Industrials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| Class A | Energy [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.40% |
| Class A | Health Care [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| Class A | Information Technology [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| Class A | Consumer Discretionary [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| Class A | Utilities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.90% |
| Class A | Real Estate [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.80% |
| Class A | Materials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| Class A | Consumer Staples [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| Class A | Communication Services [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| Class A | Short-Term Investments [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| Class C | Financials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 26.50% |
| Class C | Industrials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| Class C | Energy [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.40% |
| Class C | Health Care [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| Class C | Information Technology [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| Class C | Consumer Discretionary [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| Class C | Utilities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.90% |
| Class C | Real Estate [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.80% |
| Class C | Materials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| Class C | Consumer Staples [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| Class C | Communication Services [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| Class C | Short-Term Investments [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| Class R | Financials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 26.50% |
| Class R | Industrials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| Class R | Energy [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.40% |
| Class R | Health Care [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| Class R | Information Technology [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| Class R | Consumer Discretionary [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| Class R | Utilities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.90% |
| Class R | Real Estate [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.80% |
| Class R | Materials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| Class R | Consumer Staples [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| Class R | Communication Services [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| Class R | Short-Term Investments [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| Class I | Financials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 26.50% |
| Class I | Industrials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| Class I | Energy [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.40% |
| Class I | Health Care [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| Class I | Information Technology [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| Class I | Consumer Discretionary [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| Class I | Utilities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.90% |
| Class I | Real Estate [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.80% |
| Class I | Materials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| Class I | Consumer Staples [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| Class I | Communication Services [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| Class I | Short-Term Investments [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| Class IS | Financials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 26.50% |
| Class IS | Industrials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| Class IS | Energy [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.40% |
| Class IS | Health Care [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| Class IS | Information Technology [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| Class IS | Consumer Discretionary [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| Class IS | Utilities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.90% |
| Class IS | Real Estate [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.80% |
| Class IS | Materials [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| Class IS | Consumer Staples [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| Class IS | Communication Services [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| Class IS | Short-Term Investments [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
