v3.26.1
Shareholder Report
 6 Months Ended
Apr. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Old Westbury Funds, Inc.
Entity Central Index Key 0000909994
Entity Investment Company Type N-1A
Document Period End Date Apr. 30, 2026
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
C000004836  
Shareholder Report [Line Items]  
Fund Name All Cap Core Fund
Class Name All Cap Core Fund
Trading Symbol OWACX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury All Cap Core Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury All Cap Core Fund
$48
0.95%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 48
Expense Ratio, Percent 0.95% [1]
AssetsNet $ 3,522,700,219
Holdings Count | Holding 103
InvestmentCompanyPortfolioTurnover 25.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$3,522,700,219
  • # of Portfolio Holdings103
  • Portfolio Turnover Rate25%
Holdings [Text Block]

Sector Weightings (as a % of Net Assets) as of 4/30/2026

Table Summary
Information Technology
28.5%
Industrials
14.6%
Communication Services
11.1%
Health Care
9.2%
Financial Services
9.2%
Consumer Discretionary
6.4%
Consumer Staples
3.7%
Banks
3.4%
Other Sectors
7.7%
Other Assets and Liabilities
6.2%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
NVIDIA Corp.
7.0%
Alphabet, Inc.
5.7%
Apple, Inc.
4.5%
Microsoft Corp.
4.2%
Amazon.com, Inc.
3.8%
Broadcom, Inc.
3.4%
Meta Platforms, Inc.
2.2%
iShares MSCI EAFE ETF
2.2%
Visa, Inc.
2.0%
JP Morgan Chase & Co.
1.8%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000004835  
Shareholder Report [Line Items]  
Fund Name Large Cap Strategies Fund
Class Name Large Cap Strategies Fund
Trading Symbol OWLSX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury Large Cap Strategies Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury Large Cap Strategies Fund
$56
1.10%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 56
Expense Ratio, Percent 1.10% [2]
AssetsNet $ 25,084,259,664
Holdings Count | Holding 396
InvestmentCompanyPortfolioTurnover 36.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$25,084,259,664
  • # of Portfolio Holdings396
  • Portfolio Turnover Rate36%
Holdings [Text Block]

Sector Weightings (as a % of Net Assets) as of 4/30/2026

Table Summary
Information Technology
27.8%
Industrials
12.3%
Communication Services
10.0%
Banks
9.2%
Consumer Discretionary
9.0%
Health Care
7.5%
Consumer Staples
6.0%
Financial Services
5.5%
Other Sectors
11.4%
Other Assets and Liabilities
1.3%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
NVIDIA Corp.
6.4%
Alphabet, Inc.
5.5%
Apple, Inc.
4.2%
Amazon.com, Inc.
3.4%
Microsoft Corp.
3.4%
Broadcom, Inc.
2.9%
JP Morgan Chase & Co.
1.7%
Taiwan Semiconductor Manufacturing Co. Ltd.
1.6%
Meta Platforms, Inc.
1.6%
Chevron Corp.
1.3%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000004834  
Shareholder Report [Line Items]  
Fund Name Small & Mid Cap Strategies Fund
Class Name Small & Mid Cap Strategies Fund
Trading Symbol OWSMX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury Small & Mid Cap Strategies Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury Small & Mid Cap Strategies Fund
$58
1.10%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 58
Expense Ratio, Percent 1.10% [3]
AssetsNet $ 9,373,918,672
Holdings Count | Holding 2,297
InvestmentCompanyPortfolioTurnover 38.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$9,373,918,672
  • # of Portfolio Holdings2,297
  • Portfolio Turnover Rate38%
Holdings [Text Block]

Country Weightings (as a % of Net Assets) as of 4/30/2026

Table Summary
United States
39.5%
Japan
11.7%
China
5.6%
United Kingdom
4.1%
Australia
2.8%
South Korea
2.5%
Switzerland
2.1%
France
2.0%
Other Countries
22.6%
Other Assets and Liabilities
7.1%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
VanEck Junior Gold Miners ETF
3.3%
State Street SPDR S&P Biotech ETF
1.2%
Keysight Technologies, Inc.
0.7%
Clean Harbors, Inc.
0.6%
US Foods Holding Corp.
0.5%
Saia, Inc.
0.5%
STERIS Plc
0.5%
Nasdaq, Inc.
0.4%
API Group Corp.
0.4%
UL Solutions, Inc.
0.4%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000257451  
Shareholder Report [Line Items]  
Fund Name Total Equity Fund
Class Name Total Equity Fund
Trading Symbol OWTEX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury Total Equity Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury Total Equity Fund
$50
0.98%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 50
Expense Ratio, Percent 0.98% [4]
AssetsNet $ 1,171,475,143
Holdings Count | Holding 488
InvestmentCompanyPortfolioTurnover 31.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$1,171,475,143
  • # of Portfolio Holdings488
  • Portfolio Turnover Rate31%
Holdings [Text Block]

Sector Weightings (as a % of Net Assets) as of 4/30/2026

Table Summary
Information Technology
25.8%
Industrials
14.2%
Communication Services
9.2%
Consumer Discretionary
8.3%
Health Care
8.0%
Banks
7.7%
Financial Services
6.1%
Consumer Staples
5.5%
Other Sectors
11.0%
Other Assets and Liabilities
4.2%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
NVIDIA Corp.
5.6%
Alphabet, Inc.
4.7%
Apple, Inc.
3.5%
Microsoft Corp.
3.0%
Amazon.com, Inc.
3.0%
Broadcom, Inc.
2.5%
Meta Platforms, Inc.
1.5%
JP Morgan Chase & Co.
1.4%
Taiwan Semiconductor Manufacturing Co. Ltd.
1.4%
ASML Holding NV
1.1%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000221944  
Shareholder Report [Line Items]  
Fund Name Credit Income Fund
Class Name Credit Income Fund
Trading Symbol OWCIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury Credit Income Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury Credit Income Fund
$42
0.85%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 42
Expense Ratio, Percent 0.85% [5]
AssetsNet $ 2,540,489,364
Holdings Count | Holding 847
InvestmentCompanyPortfolioTurnover 5.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$2,540,489,364
  • # of Portfolio Holdings847
  • Portfolio Turnover Rate5%
Holdings [Text Block]

Asset Allocations (as a % of Net Assets) as of 4/30/2026

Table Summary
U.S. Government Agencies and Securities
28.8%
Non-Agency Mortgage-Backed Securities
24.9%
Exchange-Traded Funds
20.9%
Asset-Backed Securities
12.1%
Corporate Bonds
5.8%
U.S. Government Sponsored Agency Mortgage-Backed Securities
0.2%
Preferred Stocks
0.2%
Other Assets and Liabilities
7.1%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
U.S. Treasury Bonds
23.5%
iShares J.P. Morgan USD Emerging Markets Bond ETF
8.2%
Barclays Mortgage Loan Trust
6.4%
iShares MBS ETF
5.6%
U.S. Treasury Notes
5.3%
State Street SPDR Bloomberg Convertible Securities ETF
4.8%
Ajax Mortgage Loan Trust
3.4%
Invesco Preferred ETF
1.5%
Countrywide Alternative Loan Trust
1.5%
Velocity Commercial Capital Loan Trust
1.3%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000004833  
Shareholder Report [Line Items]  
Fund Name Fixed Income Fund
Class Name Fixed Income Fund
Trading Symbol OWFIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury Fixed Income Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury Fixed Income Fund
$28
0.57%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 28
Expense Ratio, Percent 0.57% [6]
AssetsNet $ 1,631,770,917
Holdings Count | Holding 144
InvestmentCompanyPortfolioTurnover 17.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$1,631,770,917
  • # of Portfolio Holdings144
  • Portfolio Turnover Rate17%
Holdings [Text Block]

Asset Allocations (as a % of Net Assets) as of 4/30/2026

Table Summary
U.S. Government Agencies and Securities
66.8%
Corporate Bonds
27.8%
Asset-Backed Securities
4.1%
Other Assets and Liabilities
1.3%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
U.S. Treasury Notes
62.8%
U.S. Treasury Inflation Indexed Bonds
4.0%
Bank of America Corp.
0.6%
JP Morgan Chase & Co.
0.6%
HCA, Inc.
0.5%
Alphabet, Inc.
0.5%
Capital One Financial Corp.
0.5%
US Bancorp
0.5%
PayPal Holdings, Inc.
0.4%
L3Harris Technologies, Inc.
0.4%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000248048  
Shareholder Report [Line Items]  
Fund Name Short-Term Bond Fund
Class Name Short-Term Bond Fund
Trading Symbol OWSBX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury Short-Term Bond Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury Short-Term Bond Fund
$18
0.37%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 18
Expense Ratio, Percent 0.37% [7]
AssetsNet $ 161,441,978
Holdings Count | Holding 131
InvestmentCompanyPortfolioTurnover 31.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$161,441,978
  • # of Portfolio Holdings131
  • Portfolio Turnover Rate31%
Holdings [Text Block]

Asset Allocations (as a % of Net Assets) as of 4/30/2026

Table Summary
U.S. Government Agencies and Securities
58.3%
Corporate Bonds
36.7%
Asset-Backed Securities
3.8%
Other Assets and Liabilities
1.2%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
U.S. Treasury Notes
52.2%
U.S. Treasury Bills
6.1%
JP Morgan Chase & Co.
1.2%
HCA, Inc.
1.0%
Hyundai Capital America
0.9%
Morgan Stanley Private Bank NA
0.9%
Roper Technologies, Inc.
0.9%
Amphenol Corp.
0.9%
Waste Management, Inc.
0.9%
AerCap Ireland Capital DAC/AerCap Global Aviation Trust
0.9%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000004838  
Shareholder Report [Line Items]  
Fund Name Municipal Bond Fund
Class Name Municipal Bond Fund
Trading Symbol OWMBX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury Municipal Bond Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury Municipal Bond Fund
$28
0.57%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 28
Expense Ratio, Percent 0.57% [8]
AssetsNet $ 4,548,197,178
Holdings Count | Holding 551
InvestmentCompanyPortfolioTurnover 13.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$4,548,197,178
  • # of Portfolio Holdings551
  • Portfolio Turnover Rate13%
Holdings [Text Block]

State Diversification (as a % of Net Assets) as of 4/30/2026

Table Summary
Texas
26.6%
New York
8.1%
New Jersey
6.8%
Washington
5.0%
Ohio
4.7%
Connecticut
3.9%
Virginia
3.6%
Massachusetts
3.4%
Other States
33.8%
Other Assets and Liabilities
4.1%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
State of Washington School Improvements GO
3.5%
Permanent University Fund - University of Texas System Current Refunding Revenue Bonds
2.3%
New York City Transitional Finance Authority Future Tax Secured Revenue Bonds
2.0%
Board of Regents of the University of Texas System Refunding Revenue Bonds
1.7%
Ohio Water Development Authority Water Utility Improvements Revenue Bonds
1.6%
Ohio Water Development Authority Water Pollution Control Loan Fund Sewer Improvements Revenue Bonds
1.4%
State of Connecticut Public Improvements GO
1.4%
New Jersey Educational Facilities Authority University & College Improvements Revenue Bonds
1.3%
Arizona Department of Transportation State Highway Improvements Revenue Bonds
1.3%
New Jersey Educational Facilities Authority Current Refunding Revenue Bonds
1.2%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000206042  
Shareholder Report [Line Items]  
Fund Name California Municipal Bond Fund
Class Name California Municipal Bond Fund
Trading Symbol OWCAX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury California Municipal Bond Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury California Municipal Bond Fund
$28
0.57%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 28
Expense Ratio, Percent 0.57% [9]
AssetsNet $ 406,470,488
Holdings Count | Holding 109
InvestmentCompanyPortfolioTurnover 11.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$406,470,488
  • # of Portfolio Holdings109
  • Portfolio Turnover Rate11%
Holdings [Text Block]

State Diversification (as a % of Net Assets) as of 4/30/2026

Table Summary
California
96.0%
Other Assets and Liabilities
4.0%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
State of California Current Refunding GO
9.6%
California Health Facilities Financing Authority Health Care Facilities Revenue Bonds
5.7%
University of California Current Refunding Revenue Bonds
5.4%
San Francisco City & County Airport Current Refunding Revenue Bonds
5.1%
University of California University & College Improvements Revenue Bonds
4.7%
California Infrastructure & Economic Development Bank Current Refunding Revenue Bonds
4.4%
San Francisco City & County Airport Comm-San Francisco International Airport & Marina Improvements Revenue Bonds
4.3%
State of California Water Utility Improvements GO
3.9%
Los Angeles Department of Water & Power Water System Revenue Bonds
3.0%
California Educational Facilities Authority University & College Improvements Revenue Bonds
2.9%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
C000206043  
Shareholder Report [Line Items]  
Fund Name New York Municipal Bond Fund
Class Name New York Municipal Bond Fund
Trading Symbol OWNYX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Old Westbury New York Municipal Bond Fund (the "Fund") for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at www.oldwestburyfunds.com. You can also request this information by contacting us at (800) 607-2200.
Additional Information Phone Number (800) 607-2200
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: 14.4px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
Expenses [Text Block]

What were the Fund costs for the last six months? 

(based on a hypothetical $10,000 investment)

Table Summary
Fund
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Old Westbury New York Municipal Bond Fund
$28
0.57%Footnote Reference*
FootnoteDescription
Footnote*
Annualized
Expenses Paid, Amount $ 28
Expense Ratio, Percent 0.57% [10]
AssetsNet $ 627,255,628
Holdings Count | Holding 163
InvestmentCompanyPortfolioTurnover 7.00%
Additional Fund Statistics [Text Block]

Fund Statistics as of 4/30/2026

  • Total Net Assets$627,255,628
  • # of Portfolio Holdings163
  • Portfolio Turnover Rate7%
Holdings [Text Block]

State Diversification (as a % of Net Assets) as of 4/30/2026

Table Summary
New York
94.6%
Other Assets and Liabilities
5.4%
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets) as of 4/30/2026

Table Summary
County of Westchester NY Recreation Facilities Improvements GO
7.8%
New York City Transitional Finance Authority Future Tax Secured Current Refunding Revenue Bonds
7.2%
New York City Transitional Finance Authority Future Tax Secured Public Improvements Revenue Bonds
6.9%
Utility Debt Securitization Authority Refunding Revenue Bonds
4.9%
New York State Dormitory Authority University & College Improvements Revenue Bonds
4.7%
City of New York Current Refunding GO
4.3%
New York State Environmental Facilities Corp. Water Utility Improvements Revenue Bonds
4.2%
Long Island Power Authority Current Refunding Revenue Bonds
3.8%
City of New York Public Improvements GO
3.6%
New York Power Authority Electric Light & Power Improvements Revenue Bonds
3.4%
Material Fund Change [Text Block]
Updated Prospectus Phone Number (800) 607-2200
Updated Prospectus Web Address <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: 14.4px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: preserve-breaks;">www.oldwestburyfunds.com</span>
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