This semi-annual shareholder report contains important information about Loomis Sayles Fixed Income Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

You can find additional information about the Fund at im.natixis.com/funddocuments. You can also request this information by contacting us at (800) 633-3330 or by contacting your financial intermediary directly.

Additional Information Phone Number

(800) 633-3330

Additional Information Website

<span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 400; grid-area: auto; line-height: 18px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">im.natixis.com/funddocuments</span>

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Institutional Class	$31	0.62%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 31

Expense Ratio, Percent

0.62%

AssetsNet

$ 470,841,920

Holdings Count | Holding

836

Advisory Fees Paid, Amount

$ 1,165,791

InvestmentCompanyPortfolioTurnover

30.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$470,841,920
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	836
Portfolio Turnover Rate	30%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$1,165,791

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	44.7%
Short-Term Investments	3.0%
Sovereigns	3.0%
ABS Car Loan	3.0%
Midstream	3.2%
Finance Companies	3.6%
Banking	3.8%
Cable Satellite	4.3%
ABS Other	5.8%
Technology	8.3%
Treasuries	17.3%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including purchased options, written options, forward foreign currency contracts and futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	2.1
US Treasury	13.3
Not rated^{Footnote Reference^}	16.1
CCC	2.0
B	5.7
BB	14.7
BBB	37.0
A	6.9
AA	1.2
AAA	1.0

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000125494

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Global Bond Fund

Class Name

Class N

Trading Symbol

LSGNX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Global Bond Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Class N	$31	0.62%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 31

Expense Ratio, Percent

0.62%

AssetsNet

$ 325,984,081

Holdings Count | Holding

327

Advisory Fees Paid, Amount

$ 690,556

InvestmentCompanyPortfolioTurnover

43.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$325,984,081
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	327
Portfolio Turnover Rate	43%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$690,556

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	35.1%
ABS Other	3.6%
Local Authorities	4.6%
Mortgage Related	5.8%
Banking	10.5%
Treasuries	40.4%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency contracts and futures contracts)

Country Weightings

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	26.1%
Mexico	3.1%
Germany	3.7%
Italy	4.5%
Canada	4.6%
United Kingdom	4.9%
France	5.0%
Spain	5.0%
Japan	6.6%
China	6.9%
United States	29.6%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency contracts and futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	1.7
US Treasury	4.2
Not rated^{Footnote Reference^}	10.4
BB	5.2
BBB	25.4
A	31.0
AA	14.4
AAA	7.3

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018127

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Global Bond Fund

Class Name

Institutional Class

Trading Symbol

LSGBX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Global Bond Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Institutional Class	$33	0.67%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 33

Expense Ratio, Percent

0.67%

AssetsNet

$ 325,984,081

Holdings Count | Holding

327

Advisory Fees Paid, Amount

$ 690,556

InvestmentCompanyPortfolioTurnover

43.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$325,984,081
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	327
Portfolio Turnover Rate	43%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$690,556

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	35.1%
ABS Other	3.6%
Local Authorities	4.6%
Mortgage Related	5.8%
Banking	10.5%
Treasuries	40.4%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency contracts and futures contracts)

Country Weightings

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	26.1%
Mexico	3.1%
Germany	3.7%
Italy	4.5%
Canada	4.6%
United Kingdom	4.9%
France	5.0%
Spain	5.0%
Japan	6.6%
China	6.9%
United States	29.6%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency contracts and futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	1.7
US Treasury	4.2
Not rated^{Footnote Reference^}	10.4
BB	5.2
BBB	25.4
A	31.0
AA	14.4
AAA	7.3

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018128

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Global Bond Fund

Class Name

Retail Class

Trading Symbol

LSGLX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Global Bond Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Retail Class	$46	0.92%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 46

Expense Ratio, Percent

0.92%

AssetsNet

$ 325,984,081

Holdings Count | Holding

327

Advisory Fees Paid, Amount

$ 690,556

InvestmentCompanyPortfolioTurnover

43.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$325,984,081
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	327
Portfolio Turnover Rate	43%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$690,556

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	35.1%
ABS Other	3.6%
Local Authorities	4.6%
Mortgage Related	5.8%
Banking	10.5%
Treasuries	40.4%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency contracts and futures contracts)

Country Weightings

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	26.1%
Mexico	3.1%
Germany	3.7%
Italy	4.5%
Canada	4.6%
United Kingdom	4.9%
France	5.0%
Spain	5.0%
Japan	6.6%
China	6.9%
United States	29.6%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including forward foreign currency contracts and futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	1.7
US Treasury	4.2
Not rated^{Footnote Reference^}	10.4
BB	5.2
BBB	25.4
A	31.0
AA	14.4
AAA	7.3

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018129

Shareholder Report [Line Items]

Fund Name

Loomis Sayles High Income Opportunities Fund

Class Name

Institutional Class

Trading Symbol

LSIOX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles High Income Opportunities Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

You can find additional information about the Fund at loomissayles.com/website/intermediary-advisory/prospectuses-and-fund-reports. You can also request this information by contacting us at (800) 633-3330 or by contacting your financial intermediary directly.

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Institutional Class	$0	0.00%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 0

Expense Ratio, Percent

0.00%

AssetsNet

$ 297,554,042

Holdings Count | Holding

428

Advisory Fees Paid, Amount

$ 0

InvestmentCompanyPortfolioTurnover

43.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$297,554,042
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	428
Portfolio Turnover Rate	43%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$0

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	46.7%
Short-Term Investments	5.8%
Lodging	3.3%
Healthcare	3.5%
Media Entertainment	3.7%
Independent Energy	4.3%
Property & Casualty Insurance	5.6%
Midstream	5.8%
Cable Satellite	9.3%
Technology	12.0%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	2.8
Not rated^{Footnote Reference^}	5.8
CCC	6.2
B	30.2
BB	53.4
BBB	0.6

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000182246

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Inflation Protected Securities Fund

Class Name

Class N

Trading Symbol

LIPNX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Inflation Protected Securities Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Class N	$17	0.35%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 17

Expense Ratio, Percent

0.35%

AssetsNet

$ 106,394,665

Holdings Count | Holding

Advisory Fees Paid, Amount

$ 0

InvestmentCompanyPortfolioTurnover

53.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$106,394,665
# of Portfolio Holdings (including overnight repurchase agreements)	52
Portfolio Turnover Rate	53%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$0

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	6.6%
Banking	3.3%
Treasuries	90.1%

Footnote	Description
Footnote^*	Net of other assets less liabilities

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	0.2
U.S. Treasury	90.2
Not rated^{Footnote Reference^}	1.4
BB	0.9
BBB	5.5
A	1.1
AA	0.5

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018130

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Inflation Protected Securities Fund

Class Name

Institutional Class

Trading Symbol

LSGSX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Inflation Protected Securities Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Institutional Class	$20	0.40%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 20

Expense Ratio, Percent

0.40%

AssetsNet

$ 106,394,665

Holdings Count | Holding

Advisory Fees Paid, Amount

$ 0

InvestmentCompanyPortfolioTurnover

53.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$106,394,665
# of Portfolio Holdings (including overnight repurchase agreements)	52
Portfolio Turnover Rate	53%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$0

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	6.6%
Banking	3.3%
Treasuries	90.1%

Footnote	Description
Footnote^*	Net of other assets less liabilities

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	0.2
U.S. Treasury	90.2
Not rated^{Footnote Reference^}	1.4
BB	0.9
BBB	5.5
A	1.1
AA	0.5

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000089752

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Inflation Protected Securities Fund

Class Name

Retail Class

Trading Symbol

LIPRX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Inflation Protected Securities Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Retail Class	$32	0.65%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 32

Expense Ratio, Percent

0.65%

AssetsNet

$ 106,394,665

Holdings Count | Holding

Advisory Fees Paid, Amount

$ 0

InvestmentCompanyPortfolioTurnover

53.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$106,394,665
# of Portfolio Holdings (including overnight repurchase agreements)	52
Portfolio Turnover Rate	53%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$0

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	6.6%
Banking	3.3%
Treasuries	90.1%

Footnote	Description
Footnote^*	Net of other assets less liabilities

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	0.2
U.S. Treasury	90.2
Not rated^{Footnote Reference^}	1.4
BB	0.9
BBB	5.5
A	1.1
AA	0.5

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018131

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Institutional High Income Fund

Class Name

Institutional Class

Trading Symbol

LSHIX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Institutional High Income Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Institutional Class	$37	0.73%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 37

Expense Ratio, Percent

0.73%

AssetsNet

$ 261,135,187

Holdings Count | Holding

441

Advisory Fees Paid, Amount

$ 732,351

InvestmentCompanyPortfolioTurnover

47.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$261,135,187
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)	441
Portfolio Turnover Rate	47%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$732,351

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	41.7%
Short-Term Investments	6.3%
Healthcare	3.1%
Chemicals	3.7%
Media Entertainment	3.9%
Independent Energy	4.0%
Property & Casualty Insurance	5.5%
Banking	5.5%
Midstream	6.1%
Cable Satellite	9.5%
Technology	10.7%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	4.9
Not rated^{Footnote Reference^}	10.5
CCC	6.2
B	30.1
BB	48.5
BBB	0.6

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000089753

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Intermediate Duration Bond Fund

Class Name

Class A

Trading Symbol

LSDRX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Intermediate Duration Bond Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

You can find additional information (including tax information) about the Fund at im.natixis.com/funddocuments. You can also request the information by contacting us at (800) 225-5478 or by contacting your financial intermediary directly.

Additional Information Phone Number

(800) 225-5478

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Class A	$33	0.65%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 33

Expense Ratio, Percent

0.65%

AssetsNet

$ 200,257,599

Holdings Count | Holding

592

Advisory Fees Paid, Amount

$ 135,141

InvestmentCompanyPortfolioTurnover

51.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$200,257,599
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)592
Portfolio Turnover Rate51%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$135,141

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	21.9%
Automotive	3.0%
Electric	3.0%
ABS Other	3.6%
Finance Companies	3.8%
Technology	3.8%
Life Insurance	5.2%
Non-Agency Commercial Mortgage-Backed Securities	7.4%
ABS Car Loan	14.5%
Banking	15.3%
Treasuries	18.5%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	0.8
US Treasury	18.6
Not rated^{Footnote Reference^}	13.6
B	0.1
BB	0.2
BBB	26.3
A	21.7
AA	6.9
AAA	12.0

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000173092

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Intermediate Duration Bond Fund

Class Name

Class C

Trading Symbol

LSCDX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Intermediate Duration Bond Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 225-5478

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Class C	$70	1.40%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 70

Expense Ratio, Percent

1.40%

AssetsNet

$ 200,257,599

Holdings Count | Holding

592

Advisory Fees Paid, Amount

$ 135,141

InvestmentCompanyPortfolioTurnover

51.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$200,257,599
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)592
Portfolio Turnover Rate51%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$135,141

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	21.9%
Automotive	3.0%
Electric	3.0%
ABS Other	3.6%
Finance Companies	3.8%
Technology	3.8%
Life Insurance	5.2%
Non-Agency Commercial Mortgage-Backed Securities	7.4%
ABS Car Loan	14.5%
Banking	15.3%
Treasuries	18.5%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	0.8
US Treasury	18.6
Not rated^{Footnote Reference^}	13.6
B	0.1
BB	0.2
BBB	26.3
A	21.7
AA	6.9
AAA	12.0

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000211126

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Intermediate Duration Bond Fund

Class Name

Class N

Trading Symbol

LSDNX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Intermediate Duration Bond Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 225-5478

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Class N	$18	0.35%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 18

Expense Ratio, Percent

0.35%

AssetsNet

$ 200,257,599

Holdings Count | Holding

592

Advisory Fees Paid, Amount

$ 135,141

InvestmentCompanyPortfolioTurnover

51.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$200,257,599
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)592
Portfolio Turnover Rate51%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$135,141

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	21.9%
Automotive	3.0%
Electric	3.0%
ABS Other	3.6%
Finance Companies	3.8%
Technology	3.8%
Life Insurance	5.2%
Non-Agency Commercial Mortgage-Backed Securities	7.4%
ABS Car Loan	14.5%
Banking	15.3%
Treasuries	18.5%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	0.8
US Treasury	18.6
Not rated^{Footnote Reference^}	13.6
B	0.1
BB	0.2
BBB	26.3
A	21.7
AA	6.9
AAA	12.0

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018132

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Intermediate Duration Bond Fund

Class Name

Class Y

Trading Symbol

LSDIX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Intermediate Duration Bond Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 225-5478

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Class Y	$20	0.40%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 20

Expense Ratio, Percent

0.40%

AssetsNet

$ 200,257,599

Holdings Count | Holding

592

Advisory Fees Paid, Amount

$ 135,141

InvestmentCompanyPortfolioTurnover

51.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Total Net Assets$200,257,599
# of Portfolio Holdings (including overnight repurchase agreements and derivatives)592
Portfolio Turnover Rate51%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)$135,141

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	21.9%
Automotive	3.0%
Electric	3.0%
ABS Other	3.6%
Finance Companies	3.8%
Technology	3.8%
Life Insurance	5.2%
Non-Agency Commercial Mortgage-Backed Securities	7.4%
ABS Car Loan	14.5%
Banking	15.3%
Treasuries	18.5%

Footnote	Description
Footnote^*	Net of other assets less liabilities (including futures contracts)

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	0.8
US Treasury	18.6
Not rated^{Footnote Reference^}	13.6
B	0.1
BB	0.2
BBB	26.3
A	21.7
AA	6.9
AAA	12.0

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018125

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Securitized Asset Fund

Class Name

Institutional Class

Trading Symbol

LSSAX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Securitized Asset Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Institutional Class	$0	0.00%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 0

Expense Ratio, Percent

0.00%

AssetsNet

$ 1,616,161,260

Holdings Count | Holding

671

Advisory Fees Paid, Amount

$ 0

InvestmentCompanyPortfolioTurnover

107.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$1,616,161,260
# of Portfolio Holdings (including overnight repurchase agreements)	671
Portfolio Turnover Rate	107%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$0

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	(17.0%)
Collateralized Loan Obligations	3.8%
ABS Home Equity	4.0%
Agency Commercial Mortgage-Backed Securities	6.2%
ABS Car Loan	7.6%
Non-Agency Commercial Mortgage-Backed Securities	9.4%
ABS Other	10.3%
Collateralized Mortgage Obligations	13.8%
Mortgage Related	61.9%

Footnote	Description
Footnote^*	Net of other assets less liabilities

Credit Quality^{Footnote Reference*}^{Footnote Reference†}

Table Summary
Value	Value
Cash & equivalents	0.3
Not rated^{Footnote Reference^}	21.7
B	0.4
BB	0.3
BBB	0.8
A	2.9
AA	84.7
AAA	9.9

Footnote	Description
Footnote^*	Percentages are calculated based on Net Assets. Totals may not add up to 100% due to other assets and liabilities, such as receivables and payables, not being included in the table.
Footnote^†	Credit ratings are by S&P Global Ratings. A credit rating is an assessment provided by a nationally recognized statistical rating organization (NRSRO) of the creditworthiness of an issuer with respect to debt obligations except for those debt obligations that are only privately rated. Ratings are measured on a scale that generally ranges from AAA (highest) to D (lowest). The credit ratings shown relate to the creditworthiness of the issuers of the underlying securities in the Fund, and not to the Fund or its shares. Credit ratings are subject to change.
Footnote^{^}	Not Rated category represents only those securities not rated by S&P Global Ratings. Such securities may be rated by other NRSROs not shown here.

Credit Quality Explanation [Text Block]

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000125495

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Small Cap Value Fund

Class Name

Class N

Trading Symbol

LSCNX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Small Cap Value Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Class N	$43	0.85%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 43

Expense Ratio, Percent

0.85%

AssetsNet

$ 325,598,965

Holdings Count | Holding

101

Advisory Fees Paid, Amount

$ 1,133,958

InvestmentCompanyPortfolioTurnover

21.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$325,598,965
# of Portfolio Holdings (including overnight repurchase agreements)	101
Portfolio Turnover Rate	21%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$1,133,958

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	45.9%
Short-Term Investments	3.0%
Health Care Providers & Services	3.4%
Oil, Gas & Consumable Fuels	3.5%
Energy Equipment & Services	4.2%
Aerospace & Defense	4.7%
Trading Companies & Distributors	4.8%
Machinery	5.2%
Capital Markets	5.2%
Electronic Equipment, Instruments & Components	7.2%
Banks	12.9%

Footnote	Description
Footnote^*	Net of other assets less liabilities

Largest Holdings [Text Block]

Top Ten Holdings

Table Summary
Moog, Inc., Class A	2.1%
Bel Fuse, Inc., Class B	1.9%
TTM Technologies, Inc.	1.8%
Popular, Inc.	1.8%
Kodiak Gas Services, Inc.	1.8%
Ameris Bancorp	1.6%
Viper Energy, Inc., Class A	1.6%
Array Digital Infrastructure, Inc.	1.6%
Garrett Motion, Inc.	1.5%
TD SYNNEX Corp.	1.5%

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018134

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Small Cap Value Fund

Class Name

Institutional Class

Trading Symbol

LSSCX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Small Cap Value Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Institutional Class	$46	0.90%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 46

Expense Ratio, Percent

0.90%

AssetsNet

$ 325,598,965

Holdings Count | Holding

101

Advisory Fees Paid, Amount

$ 1,133,958

InvestmentCompanyPortfolioTurnover

21.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$325,598,965
# of Portfolio Holdings (including overnight repurchase agreements)	101
Portfolio Turnover Rate	21%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$1,133,958

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	45.9%
Short-Term Investments	3.0%
Health Care Providers & Services	3.4%
Oil, Gas & Consumable Fuels	3.5%
Energy Equipment & Services	4.2%
Aerospace & Defense	4.7%
Trading Companies & Distributors	4.8%
Machinery	5.2%
Capital Markets	5.2%
Electronic Equipment, Instruments & Components	7.2%
Banks	12.9%

Footnote	Description
Footnote^*	Net of other assets less liabilities

Largest Holdings [Text Block]

Top Ten Holdings

Table Summary
Moog, Inc., Class A	2.1%
Bel Fuse, Inc., Class B	1.9%
TTM Technologies, Inc.	1.8%
Popular, Inc.	1.8%
Kodiak Gas Services, Inc.	1.8%
Ameris Bancorp	1.6%
Viper Energy, Inc., Class A	1.6%
Array Digital Infrastructure, Inc.	1.6%
Garrett Motion, Inc.	1.5%
TD SYNNEX Corp.	1.5%

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018135

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Small Cap Value Fund

Class Name

Retail Class

Trading Symbol

LSCRX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Small Cap Value Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Retail Class	$58	1.15%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 58

Expense Ratio, Percent

1.15%

AssetsNet

$ 325,598,965

Holdings Count | Holding

101

Advisory Fees Paid, Amount

$ 1,133,958

InvestmentCompanyPortfolioTurnover

21.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$325,598,965
# of Portfolio Holdings (including overnight repurchase agreements)	101
Portfolio Turnover Rate	21%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$1,133,958

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	45.9%
Short-Term Investments	3.0%
Health Care Providers & Services	3.4%
Oil, Gas & Consumable Fuels	3.5%
Energy Equipment & Services	4.2%
Aerospace & Defense	4.7%
Trading Companies & Distributors	4.8%
Machinery	5.2%
Capital Markets	5.2%
Electronic Equipment, Instruments & Components	7.2%
Banks	12.9%

Footnote	Description
Footnote^*	Net of other assets less liabilities

Largest Holdings [Text Block]

Top Ten Holdings

Table Summary
Moog, Inc., Class A	2.1%
Bel Fuse, Inc., Class B	1.9%
TTM Technologies, Inc.	1.8%
Popular, Inc.	1.8%
Kodiak Gas Services, Inc.	1.8%
Ameris Bancorp	1.6%
Viper Energy, Inc., Class A	1.6%
Array Digital Infrastructure, Inc.	1.6%
Garrett Motion, Inc.	1.5%
TD SYNNEX Corp.	1.5%

Material Fund Change [Text Block]

Material Fund Changes

There were no material fund changes during the period.

Summary of Change Legend [Text Block]

There were no material fund changes during the period.

C000018136

Shareholder Report [Line Items]

Fund Name

Loomis Sayles Small Cap Value Fund

Class Name

Admin Class

Trading Symbol

LSVAX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Loomis Sayles Small Cap Value Fund for the period of October 1, 2025 to March 31, 2026.

Additional Information [Text Block]

Additional Information Phone Number

(800) 633-3330

Additional Information Website

Expenses [Text Block]

What were the fund 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^{Footnote Reference†}
Admin Class	$71	1.40%

Footnote	Description
Footnote^†	Annualized for periods less than one year (if applicable).

Expenses Paid, Amount

$ 71

Expense Ratio, Percent

1.40%

AssetsNet

$ 325,598,965

Holdings Count | Holding

101

Advisory Fees Paid, Amount

$ 1,133,958

InvestmentCompanyPortfolioTurnover

21.00%

Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Total Net Assets	$325,598,965
# of Portfolio Holdings (including overnight repurchase agreements)	101
Portfolio Turnover Rate	21%
Total Advisory Fees Paid (after waiver/reimbursement, if applicable)	$1,133,958

Holdings [Text Block]

Industry Summary

Table Summary
Value	Value
Other investments less than 3% of net assets^{Footnote Reference*}	45.9%
Short-Term Investments	3.0%
Health Care Providers & Services	3.4%
Oil, Gas & Consumable Fuels	3.5%
Energy Equipment & Services	4.2%
Aerospace & Defense	4.7%
Trading Companies & Distributors	4.8%
Machinery	5.2%
Capital Markets	5.2%
Electronic Equipment, Instruments & Components	7.2%
Banks	12.9%

Footnote	Description
Footnote^*	Net of other assets less liabilities

Largest Holdings [Text Block]

Top Ten Holdings

Table Summary
Moog, Inc., Class A	2.1%
Bel Fuse, Inc., Class B	1.9%
TTM Technologies, Inc.	1.8%
Popular, Inc.	1.8%
Kodiak Gas Services, Inc.	1.8%
Ameris Bancorp	1.6%
Viper Energy, Inc., Class A	1.6%
Array Digital Infrastructure, Inc.	1.6%
Garrett Motion, Inc.	1.5%
TD SYNNEX Corp.	1.5%

Material Fund Change [Text Block]

Material Fund Changes

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Summary of Change Legend [Text Block]

There were no material fund changes during the period.

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Country Weightings

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Country Weightings

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Country Weightings

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Credit QualityFootnote Reference*Footnote Reference†

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Top Ten Holdings

Material Fund Changes

What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)

Key Fund Statistics

Industry Summary

Top Ten Holdings

Material Fund Changes

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