v3.26.1
Shareholder Report
 6 Months Ended
Apr. 30, 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 Apr. 30, 2026
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Class 1  
Shareholder Report [Line Items]  
Fund Name ClearBridge Mid Cap Fund
Class Name Class 1
Trading Symbol SMCPX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about ClearBridge Mid Cap Fund for the period November 1, 2025, to April 30, 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 1
$43
0.84%
[1],[2]
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.84%
Net Assets $ 1,580,121,349
Holdings Count | $ / shares 63
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$1,580,121,349
Total Number of Portfolio Holdings
63
Portfolio Turnover Rate
26%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition* (% of Total Investments)
image
 [3]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class A  
Shareholder Report [Line Items]  
Fund Name ClearBridge Mid Cap Fund
Class Name Class A
Trading Symbol SBMAX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about ClearBridge Mid Cap Fund for the period November 1, 2025, to April 30, 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 A
$58
1.14%
[4],[5]
Expenses Paid, Amount $ 58
Expense Ratio, Percent 1.14%
Net Assets $ 1,580,121,349
Holdings Count | $ / shares 63
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$1,580,121,349
Total Number of Portfolio Holdings
63
Portfolio Turnover Rate
26%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition* (% of Total Investments)
image
 [6]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class C  
Shareholder Report [Line Items]  
Fund Name ClearBridge Mid Cap Fund
Class Name Class C
Trading Symbol SBMLX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about ClearBridge Mid Cap Fund for the period November 1, 2025, to April 30, 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 C
$96
1.90%
[7],[8]
Expenses Paid, Amount $ 96
Expense Ratio, Percent 1.90%
Net Assets $ 1,580,121,349
Holdings Count | $ / shares 63
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$1,580,121,349
Total Number of Portfolio Holdings
63
Portfolio Turnover Rate
26%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition* (% of Total Investments)
image
 [9]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class R  
Shareholder Report [Line Items]  
Fund Name ClearBridge Mid Cap Fund
Class Name Class R
Trading Symbol LMREX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about ClearBridge Mid Cap Fund for the period November 1, 2025, to April 30, 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 R
$73
1.45%
[10],[11]
Expenses Paid, Amount $ 73
Expense Ratio, Percent 1.45%
Net Assets $ 1,580,121,349
Holdings Count | $ / shares 63
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$1,580,121,349
Total Number of Portfolio Holdings
63
Portfolio Turnover Rate
26%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition* (% of Total Investments)
image
 [12]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class I  
Shareholder Report [Line Items]  
Fund Name ClearBridge Mid Cap Fund
Class Name Class I
Trading Symbol SMBYX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about ClearBridge Mid Cap Fund for the period November 1, 2025, to April 30, 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
$43
0.84%
[13],[14]
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.84%
Net Assets $ 1,580,121,349
Holdings Count | $ / shares 63
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$1,580,121,349
Total Number of Portfolio Holdings
63
Portfolio Turnover Rate
26%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition* (% of Total Investments)
image
 [15]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class IS  
Shareholder Report [Line Items]  
Fund Name ClearBridge Mid Cap Fund
Class Name Class IS
Trading Symbol LSIRX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about ClearBridge Mid Cap Fund for the period November 1, 2025, to April 30, 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
$38
0.75%
[16],[17]
Expenses Paid, Amount $ 38
Expense Ratio, Percent 0.75%
Net Assets $ 1,580,121,349
Holdings Count | $ / shares 63
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$1,580,121,349
Total Number of Portfolio Holdings
63
Portfolio Turnover Rate
26%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition* (% of Total Investments)
image
 [18]
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.  
[10]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[11]
† Annualized.
[12]
* Does not include derivatives, except purchased options, if any.  
[13]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[14]
† Annualized.
[15]
* Does not include derivatives, except purchased options, if any.  
[16]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[17]
† Annualized.
[18]
* Does not include derivatives, except purchased options, if any.