S000006705 [Member] Annual Fund Operating Expenses - Loomis Sayles Small Cap Growth Fund	Sep. 30, 2025
Prospectus [Line Items]
Fee Waiver or Reimbursement over Assets, Date of Termination	January 31, 2027
Institutional Class
Prospectus [Line Items]
Management Fees (as a percentage of Assets)	0.75%
Distribution and Service (12b-1) Fees	0.00%
Other Expenses (as a percentage of Assets):	0.18%	[1]
Expenses (as a percentage of Assets)	0.93%
Fee Waiver or Reimbursement	0.00%	[2]
Net Expenses (as a percentage of Assets)	0.93%
Retail Class
Prospectus [Line Items]
Management Fees (as a percentage of Assets)	0.75%
Distribution and Service (12b-1) Fees	0.25%
Other Expenses (as a percentage of Assets):	0.18%
Expenses (as a percentage of Assets)	1.18%
Fee Waiver or Reimbursement	0.00%	[2]
Net Expenses (as a percentage of Assets)	1.18%
Class N
Prospectus [Line Items]
Management Fees (as a percentage of Assets)	0.75%
Distribution and Service (12b-1) Fees	0.00%
Other Expenses (as a percentage of Assets):	0.07%
Expenses (as a percentage of Assets)	0.82%
Fee Waiver or Reimbursement	0.00%	[2]
Net Expenses (as a percentage of Assets)	0.82%

[1] Pursuant to an expense offset arrangement, credits realized as a result of uninvested cash balances may be used to reduce the Fund’s transfer agent expenses. Other expenses are shown net of such reductions of transfer agent expenses of 1 bps.

[2] Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.20% and 0.90% of the Fund’s average daily net assets for Institutional Class shares, Retail Class shares and Class N shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2027 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class-by-class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation at the time such amounts were waived/reimbursed and (2) the class’ current applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.