| Label | Element | Value |
|---|---|---|
| Old Westbury California Municipal Bond Fund | Old Westbury California Municipal Bond Fund | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk/Return [Heading] | oef_RiskReturnHeading | Old Westbury New York Municipal Bond Fund |
| Expense Heading [Optional Text] | oef_ExpenseHeading | Old Westbury California Municipal Bond Fund |
| Fee Waiver or Reimbursement over Assets, Date of Termination | oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination | Oct. 31, 2028 |
| Supplement to Prospectus [Text Block] | oef_SupplementToProspectusTextBlock | Old Westbury All Cap Core Fund Old Westbury Large Cap Strategies Fund Old Westbury Small & Mid Cap Strategies Fund Old Westbury Total Equity Fund Old Westbury Credit Income Fund Old Westbury Fixed Income Fund Old Westbury Short-Term Bond Fund Old Westbury Municipal Bond Fund Old Westbury California Municipal Bond Fund Old Westbury New York Municipal Bond Fund
Supplement dated October 1, 2026 to the |