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 New Alternatives Fund
Entity Central Index Key 0000355767
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
C000013290  
Shareholder Report [Line Items]  
Fund Name New Alternatives Fund
Class Name Class A
Trading Symbol NALFX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about New Alternatives Fund for the period of January 1, 2026 to June 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.newalternativesfund.com/. You can also request this information by contacting us at 800-423-8383.
Additional Information Phone Number 800-423-8383
Additional Information Website https://www.newalternativesfund.com/
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 investment
Class A
$47
0.88%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 47
Expense Ratio, Percent 0.88% [1]
AssetsNet $ 314,699,449
Holdings Count | Holding 48
Advisory Fees Paid, Amount $ 800,033
InvestmentCompanyPortfolioTurnover 2.00%
Additional Fund Statistics [Text Block]

Fund Statistics 

Table Summary
Net Assets
$314,699,449
Number of Portfolio Holdings
48
Advisory Fee
$800,033
Portfolio Turnover
2%
Holdings [Text Block]

Sector Weighting (% of net assets)

Group By Asset Type Chart
Table Summary
Value
Value
Certificate of Deposit
0.1%
Natural & Organic Foods
0.7%
Recycling & Waste Management
0.8%
Transportation
1.9%
Energy Storage
2.6%
Solar Photovoltaic
3.9%
Sustainable Energy Financial Services
5.0%
Wind Turbines
5.0%
Water Systems
6.5%
Energy Conservation
9.8%
Energy Management
13.4%
Utilities
19.7%
Renewable Energy Power Producers & Developers
24.8%

Top 10 Holdings (% of net assets)

Table Summary
Holding Name
% of Net Assets
Iberdrola S.A.
5.6%
Acciona S.A.
5.5%
Veolia Environnement S.A.
5.3%
Enel SpA
5.1%
Siemens A.G.
5.1%
Infratil Ltd.
5.0%
HA Sustainable Infrastructure Capital, Inc.
5.0%
Terna - Rete Elettrica Nazionale
4.8%
Brookfield Renewable Corporation
4.7%
Clearway Energy, Inc., Class C
4.4%
C000146229  
Shareholder Report [Line Items]  
Fund Name New Alternatives Fund
Class Name Investor Class
Trading Symbol NAEFX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about New Alternatives Fund for the period of January 1, 2026 to June 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.newalternativesfund.com/. You can also request this information by contacting us at 800-423-8383.
Additional Information Phone Number 800-423-8383
Additional Information Website https://www.newalternativesfund.com/
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 investment
Investor
$61
1.12%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 61
Expense Ratio, Percent 1.12% [2]
AssetsNet $ 314,699,449
Holdings Count | Holding 48
Advisory Fees Paid, Amount $ 800,033
InvestmentCompanyPortfolioTurnover 2.00%
Additional Fund Statistics [Text Block]

Fund Statistics 

Table Summary
Net Assets
$314,699,449
Number of Portfolio Holdings
48
Advisory Fee
$800,033
Portfolio Turnover
2%
Holdings [Text Block]

Sector Weighting (% of net assets)

Group By Asset Type Chart
Table Summary
Value
Value
Certificate of Deposit
0.1%
Natural & Organic Foods
0.7%
Recycling & Waste Management
0.8%
Transportation
1.9%
Energy Storage
2.6%
Solar Photovoltaic
3.9%
Sustainable Energy Financial Services
5.0%
Wind Turbines
5.0%
Water Systems
6.5%
Energy Conservation
9.8%
Energy Management
13.4%
Utilities
19.7%
Renewable Energy Power Producers & Developers
24.8%

Top 10 Holdings (% of net assets)

Table Summary
Holding Name
% of Net Assets
Iberdrola S.A.
5.6%
Acciona S.A.
5.5%
Veolia Environnement S.A.
5.3%
Enel SpA
5.1%
Siemens A.G.
5.1%
Infratil Ltd.
5.0%
HA Sustainable Infrastructure Capital, Inc.
5.0%
Terna - Rete Elettrica Nazionale
4.8%
Brookfield Renewable Corporation
4.7%
Clearway Energy, Inc., Class C
4.4%
[1] Annualized
[2] Annualized