v3.26.1
Shareholder Report
 6 Months Ended
May 31, 2026
USD ($)
$ / shares
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Legg Mason Partners Investment Trust
Entity Central Index Key 0000880366
Entity Investment Company Type N-1A
Document Period End Date May 31, 2026
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Class FI  
Shareholder Report [Line Items]  
Fund Name Franklin U.S. Large Cap Equity Fund
Class Name Class FI
Trading Symbol LMUSX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Franklin U.S. Large Cap Equity Fund for the period  December 1, 2025, to May 31, 2026.
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 FI
$55
1.05%
[1],[2]
Expenses Paid, Amount $ 55
Expense Ratio, Percent 1.05%
Net Assets $ 532,087,360
Holdings Count | $ / shares 120
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of May 31, 2026)
Total Net Assets
$532,087,360
Total Number of Portfolio Holdings
120
Portfolio Turnover Rate
22%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of May 31, 2026)
Portfolio Composition* (% of Total Investments)
image
 [3]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class I  
Shareholder Report [Line Items]  
Fund Name Franklin U.S. Large Cap Equity Fund
Class Name Class I
Trading Symbol LMTIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Franklin U.S. Large Cap Equity Fund for the period  December 1, 2025, to May 31, 2026.
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
$42
0.80%
[4],[5]
Expenses Paid, Amount $ 42
Expense Ratio, Percent 0.80%
Net Assets $ 532,087,360
Holdings Count | $ / shares 120
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of May 31, 2026)
Total Net Assets
$532,087,360
Total Number of Portfolio Holdings
120
Portfolio Turnover Rate
22%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of May 31, 2026)
Portfolio Composition* (% of Total Investments)
image
 [6]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class IS  
Shareholder Report [Line Items]  
Fund Name Franklin U.S. Large Cap Equity Fund
Class Name Class IS
Trading Symbol LMISX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Franklin U.S. Large Cap Equity Fund for the period  December 1, 2025, to May 31, 2026.
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
$37
0.70%
[7],[8]
Expenses Paid, Amount $ 37
Expense Ratio, Percent 0.70%
Net Assets $ 532,087,360
Holdings Count | $ / shares 120
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of May 31, 2026)
Total Net Assets
$532,087,360
Total Number of Portfolio Holdings
120
Portfolio Turnover Rate
22%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of May 31, 2026)
Portfolio Composition* (% of Total Investments)
image
 [9]
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.
[2]
† Annualized.
[3]
* Does not include derivatives, except purchased options, if any.  
[4]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[5]
† Annualized.
[6]
* Does not include derivatives, except purchased options, if any.  
[7]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[8]
† Annualized.
[9]
* Does not include derivatives, except purchased options, if any.