v3.26.1
Shareholder Report
 6 Months Ended
Jun. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name IMPAX FUNDS SERIES TRUST III
Entity Central Index Key 0001598735
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
C000141748  
Shareholder Report [Line Items]  
Fund Name Impax Global Women's Leadership Fund
Class Name Investor Class
Trading Symbol PXWEX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Impax Global Women's Leadership Fund (the "Fund") (formerly known as Impax Ellevate Global Women's Leadership Fund) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-annual Shareholder Report
Additional Information [Text Block] You can also request this information by contacting us at (800) 372-7827.
Additional Information Phone Number (800) 372-7827
Expenses [Text Block]

What were the Fund's costs for the last six months? 

(based on a hypothetical $10,000 investment) 

Table Summary
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investmentFootnote Reference*
Investor Class
$40
0.78%
FootnoteDescription
Footnote*
Annualized.
Expenses Paid, Amount $ 40
Expense Ratio, Percent 0.78%
AssetsNet $ 651,845,760
Holdings Count | Holding 107
InvestmentCompanyPortfolioTurnover 12.00%
Additional Fund Statistics [Text Block]

Key Fund Statistics as of June 30, 2026

Table Summary
Net Assets
$651,845,760
Total Number of Portfolio Holdings
107
Portfolio Turnover Rate
12%
Holdings [Text Block]

Sector Diversification as of June 30, 2026Footnote Reference *Footnote Reference ^

Group By Industry Chart
Table Summary
Value
Value
Other assets and liabilities (net)
1.3%
Utilities
2.2%
Materials
3.4%
Consumer Staples
6.1%
Communication Services
8.5%
Industrials
8.5%
Consumer Discretionary
10.0%
Health Care
11.5%
Financials
18.1%
Information Technology
30.4%
FootnoteDescription
Footnote *
May include companies representing multiple industries within a single “Sector”.
Footnote ^
Percent of Net Assets.

Geographical Diversification as of June 30, 2026Footnote Reference ^

Group By Country Chart
Table Summary
Value
Value
Other assets and liabilities (net)
1.3%
OthersFootnote Reference‡
1.0%
Norway
0.8%
Japan
0.8%
Italy
0.9%
Germany
1.0%
Finland
1.2%
Canada
4.7%
Australia
5.2%
France
5.9%
United Kingdom
5.9%
United States
71.3%
FootnoteDescription
Footnote ^
Percent of Net Assets.
Footnote‡
Includes additional countries outside the top 10 listed above.

Asset Allocation as of June 30, 2026Footnote Reference ^

Group By Asset Type Chart
Table Summary
Value
Value
U.S. Stocks
71.4%
Foreign Stocks
27.5%
Cash & Cash Equivalents
1.1%
FootnoteDescription
Footnote ^
Percent of Total Investments.
Largest Holdings [Text Block]

Top Ten Holdings as of June 30, 2026Footnote Reference*

Table Summary
Company
Percent of Net Assets
NVIDIA Corp.
5.9%
Apple, Inc.
4.7%
Microsoft Corp.
3.3%
Amazon.com, Inc.
2.0%
Alphabet, Inc., A
1.9%
JPMorgan Chase & Co.
1.9%
Eli Lilly & Co.
1.9%
Johnson & Johnson
1.7%
Intel Corp.
1.6%
Lam Research Corp.
1.6%
FootnoteDescription
Footnote*
Ten largest holdings do not include money market securities, certificates of deposit, commercial paper or cash and equivalents, if applicable. Holdings are subject to change.
Material Fund Change [Text Block]

Material Fund Changes

On December 4, 2025, the Fund's Board approved a name change for the Fund from Impax Ellevate Global Women's Leadership Fund to Impax Global Women's Leadership Fund. This change became effective on May 1, 2026.
C000141747  
Shareholder Report [Line Items]  
Fund Name Impax Global Women's Leadership Fund
Class Name Institutional Class
Trading Symbol PXWIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Impax Global Women's Leadership Fund (the "Fund") (formerly known as Impax Ellevate Global Women's Leadership Fund) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-annual Shareholder Report
Additional Information [Text Block] You can also request this information by contacting us at (800) 372-7827.
Additional Information Phone Number (800) 372-7827
Expenses [Text Block]

What were the Fund's costs for the last six months? 

(based on a hypothetical $10,000 investment) 

Table Summary
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investmentFootnote Reference*
Institutional Class
$27
0.53%
FootnoteDescription
Footnote*
Annualized.
Expenses Paid, Amount $ 27
Expense Ratio, Percent 0.53%
AssetsNet $ 651,845,760
Holdings Count | Holding 107
InvestmentCompanyPortfolioTurnover 12.00%
Additional Fund Statistics [Text Block]

Key Fund Statistics as of June 30, 2026

Table Summary
Net Assets
$651,845,760
Total Number of Portfolio Holdings
107
Portfolio Turnover Rate
12%
Holdings [Text Block]

Sector Diversification as of June 30, 2026Footnote Reference *Footnote Reference ^

Group By Industry Chart
Table Summary
Value
Value
Other assets and liabilities (net)
1.3%
Utilities
2.2%
Materials
3.4%
Consumer Staples
6.1%
Communication Services
8.5%
Industrials
8.5%
Consumer Discretionary
10.0%
Health Care
11.5%
Financials
18.1%
Information Technology
30.4%
FootnoteDescription
Footnote *
May include companies representing multiple industries within a single “Sector”.
Footnote ^
Percent of Net Assets.

Geographical Diversification as of June 30, 2026Footnote Reference ^

Group By Country Chart
Table Summary
Value
Value
Other assets and liabilities (net)
1.3%
OthersFootnote Reference‡
1.0%
Norway
0.8%
Japan
0.8%
Italy
0.9%
Germany
1.0%
Finland
1.2%
Canada
4.7%
Australia
5.2%
France
5.9%
United Kingdom
5.9%
United States
71.3%
FootnoteDescription
Footnote ^
Percent of Net Assets.
Footnote‡
Includes additional countries outside the top 10 listed above.

Asset Allocation as of June 30, 2026Footnote Reference ^

Group By Asset Type Chart
Table Summary
Value
Value
U.S. Stocks
71.4%
Foreign Stocks
27.5%
Cash & Cash Equivalents
1.1%
FootnoteDescription
Footnote ^
Percent of Total Investments.
Largest Holdings [Text Block]

Top Ten Holdings as of June 30, 2026Footnote Reference*

Table Summary
Company
Percent of Net Assets
NVIDIA Corp.
5.9%
Apple, Inc.
4.7%
Microsoft Corp.
3.3%
Amazon.com, Inc.
2.0%
Alphabet, Inc., A
1.9%
JPMorgan Chase & Co.
1.9%
Eli Lilly & Co.
1.9%
Johnson & Johnson
1.7%
Intel Corp.
1.6%
Lam Research Corp.
1.6%
FootnoteDescription
Footnote*
Ten largest holdings do not include money market securities, certificates of deposit, commercial paper or cash and equivalents, if applicable. Holdings are subject to change.
Material Fund Change [Text Block]

Material Fund Changes

On December 4, 2025, the Fund's Board approved a name change for the Fund from Impax Ellevate Global Women's Leadership Fund to Impax Global Women's Leadership Fund. This change became effective on May 1, 2026.