v3.25.1
Label Element Value
William Blair Small Cap Value Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading WILLIAM BLAIR SMALL CAP VALUE FUND SUMMARY
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE:
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The William Blair Small Cap Value Fund seeks long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading FEES AND EXPENSES:
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment):
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination April 30, 2026
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover:
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 35% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 35.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example:
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading PRINCIPAL INVESTMENT STRATEGIES:
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized (“small cap”) companies. For purposes of the Fund, the Adviser considers a company to be a small cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2000® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and value prospects similar to small cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell 2000® Index. The Fund may invest in equity securities listed on a national securities exchange or traded in the over‑the‑counter markets. The Fund invests primarily in common stocks, but it may also invest in other types of equity securities, including real estate investment trusts (“REITs”) and American Depositary Receipts (“ADRs”).
The Russell 2000® Index is a widely recognized, unmanaged index of common stocks that measures the performance of the 2,000 smallest companies in the Russell 3000® Index. The companies in the Russell 2000® Index are considered representative of small cap companies. The size of companies in the Russell 2000® Index may change with market conditions. In addition, changes to the composition of the Russell 2000® Index can change the market capitalization range of the companies included in the index. As of March 31, 2025, the Russell 2000® Index included securities issued by companies that ranged in size between $5.2 million and $14.96 billion. The Russell 2000® Value Index, the Fund’s performance benchmark, measures the performance of those Russell 2000 companies with lower price‑to‑book ratios and lower forecasted growth values.
In selecting investments for the Fund, the Adviser typically looks to invest in companies with leading market share positions, shareholder oriented managements, and strong balance sheet and cash flow ratios. Usually, the shares of the companies the Adviser buys are selling at a price to earnings ratio below the average price to earnings ratio of the stocks that comprise the Russell 2000® Index. In addition, the companies selected by the Adviser usually have higher returns on equity and capital than the average company in the Russell 2000® Index. The Adviser screens the Fund’s universe of potential investments to identify potentially undervalued securities based on factors such as financial strength, earnings valuation, and earnings quality. The Adviser further narrows the list of potential investments through traditional fundamental security analysis, which may include interviews with company management and a review of the assessments and opinions of outside analysts and consultants. Securities are sold when the Adviser believes the shares have become relatively overvalued or it finds more attractive alternatives. The Adviser generally will not sell a security merely due to market appreciation outside the Fund’s target capitalization range if it believes the company has valuation upside potential.
Risk [Heading] rr_RiskHeading PRINCIPAL RISKS:
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading FUND PERFORMANCE HISTORY:
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of marketperformance and an additional index. The Russell 3000® Index represents a broad measure of market performance, while the Russell 2000® Value Index is generally representative of the market sectors or types of investments in which the Fund invests. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. On July 16, 2021, the Fund acquired the assets and assumed the liabilities of the ICM Small Company Portfolio (the “Predecessor Fund”), a series of The Advisors’ Inner Circle Fund, in a reorganization (the “Reorganization”). In the Reorganization, former shareholders of the Predecessor Fund received Class I shares of the Fund. The Predecessor Fund was advised by Investment Counselors of Maryland, LLC, which was acquired by the Adviser. The Predecessor Fund’s (Institutional Class shares) performance and financial history have been adopted by Class I shares of the Fund following the Reorganization and are being used going forward from the date of the Reorganization. The performance of Class I shares of the Fund therefore reflects the performance of the Predecessor Fund prior to the Reorganization. The performance of the Predecessor Fund has not been restated to reflect the annual operating expenses of Class I shares of the Fund, which were different than those of the Predecessor Fund. Because the Fund had different fees and expenses than the Predecessor Fund, the Predecessor Fund would therefore have had different performance results if it was subject to the Fund’s fees and expenses. The Fund’s past performance (including the performance of the Predecessor Fund), before and after taxes, is not necessarily an indication of how the Fund will perform in the future and does not guarantee future results. For more recent performance information, go to www.williamblairfunds.com or call 1‑800‑635‑2886.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of marketperformance and an additional index.
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of marketperformance and an additional index.The Russell 3000® Index represents a broad measure of market performance, while the Russell 2000® Value Index is generally representative of the market sectors or types of investments in which the Fund invests.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1‑800‑635‑2886
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.williamblairfunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns.
Bar Chart Narrative [Text Block] rr_BarChartNarrativeTextBlock The bar chart below provides an illustration of how the Fund’s Class I shares performance has varied in each of the last ten calendar years.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Highest Quarterly Return29.75%(4Q20)Lowest QuarterlyReturn(35.02)%(1Q20)
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (For the periods ended December 31, 2024).
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After‑tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After‑tax returns are not relevant to investors who hold their Fund shares through tax‑deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The table below shows returns on a before‑tax and after‑tax basis for Class I shares and on a before‑tax basis for Class N and Class R6 shares. After‑tax returns for Class N and Class R6 shares will vary.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock The table below shows returns on a before‑tax and after‑tax basis for Class I shares and on a before‑tax basis for Class N and Class R6 shares. After‑tax returns for Class N and Class R6 shares will vary. After‑tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after‑tax returns depend on an investor’s tax situation and may differ from those shown. After‑tax returns are not relevant to investors who hold their Fund shares through tax‑deferred arrangements, such as 401(k) plans or individual retirement accounts.
William Blair Small Cap Value Fund | Risk Lose Money [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock The Fund’s returns will vary, and you could lose money by investing in the Fund.
William Blair Small Cap Value Fund | Equity Funds General Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Equity Funds General Risk.The value of equity securities the Fund holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.
William Blair Small Cap Value Fund | Market Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Market Risk. The value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably. The value of an investment may decline due to factors affecting securities markets generally or particular industries represented in the securities markets. The value of an investment may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, recessions, inflation, rapid interest rate changes, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Events such as war, geopolitical risk, acts of terrorism, social unrest, tariffs and other restrictions on trade, natural disasters, the spread of infectious illness or other public health threats, or the threat or potential of one or more such events and developments could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive
conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.
William Blair Small Cap Value Fund | Small and Micro Cap Company Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Small and Micro Cap Company Risk. Stocks of small and micro cap companies involve greater risk than those of larger, more established companies. This is because small and micro cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and micro cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and micro cap companies may be more volatile and less liquid than securities of large capitalized companies. For purposes of the Fund, micro cap companies are companies with market capitalizations of $500 million or less at the time of the Fund’s investment.
William Blair Small Cap Value Fund | REIT Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
REIT Risk. REITs are pooled investment vehicles that own, and usually operate, income-producing real estate. REITs are susceptible to the risks associated with direct ownership of real estate, such as the following: declines in property values; increases in property taxes, operating expenses, interest rates or competition; overbuilding; zoning changes; and losses from casualty or condemnation. REITs typically incur fees that are separate from those of the Fund. Accordingly, the Fund’s shareholders will indirectly bear a proportionate share of the REITs’ operating expenses, in addition to paying Fund expenses. REIT operating expenses are not reflected in the fee table and example in this Prospectus.
William Blair Small Cap Value Fund | Foreign Investment Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Foreign Investment Risk. The Fund’s investments in ADRs are subject to foreign securities risk. ADRs are certificates evidencing ownership of shares of a foreign issuer that are issued by depositary banks and traded on U.S. exchanges. Although ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies, they continue to be subject to many of the risks associated with investing directly in foreign securities.
William Blair Small Cap Value Fund | Share Ownership Concentration Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Share Ownership Concentration Risk. To the extent that a significant portion of the Fund’s shares is held by a limited number of shareholders or their affiliates, there is a risk that the share trading activities of these shareholders could disrupt the Fund’s investment strategies, which could have adverse consequences for the Fund and other shareholders (e.g., by requiring the Fund to sell investments at inopportune times or causing the Fund to maintain larger-than-expected cash positions pending acquisition of investments).
William Blair Small Cap Value Fund | Style Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the value investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.
William Blair Small Cap Value Fund | Focus Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Focus Risk. To the extent that the Fund focuses its investments in particular industries, asset classes or sectors of the economy, any market changes affecting companies in those industries, asset classes or sectors may impact the Fund’s performance.
William Blair Small Cap Value Fund | Operational and Technology Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Operational and Technology Risk. Cyber-attacks, disruptions, or failures that affect the Fund’s service providers, counterparties, market participants, or issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.
William Blair Small Cap Value Fund | Class N  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Redemption Fee rr_RedemptionFeeOverRedemption none
Management Fee rr_ManagementFeesOverAssets 0.75%
Distribution (Rule 12b-1) Fee rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.15%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.15%
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets [1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 1.15%
1 Year rr_ExpenseExampleYear01 $ 117
3 Years rr_ExpenseExampleYear03 365
5 Years rr_ExpenseExampleYear05 633
10 Years rr_ExpenseExampleYear10 $ 1,398
1 Year rr_AverageAnnualReturnYear01 3.21%
Since Share Class Inception rr_AverageAnnualReturnSinceInception 2.76%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 19, 2021
William Blair Small Cap Value Fund | Class I  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Redemption Fee rr_RedemptionFeeOverRedemption none
Management Fee rr_ManagementFeesOverAssets 0.75%
Distribution (Rule 12b-1) Fee rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.92%
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.03% [1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 0.89%
1 Year rr_ExpenseExampleYear01 $ 91
3 Years rr_ExpenseExampleYear03 290
5 Years rr_ExpenseExampleYear05 506
10 Years rr_ExpenseExampleYear10 $ 1,129
2015 rr_AnnualReturn2015 (3.20%)
2016 rr_AnnualReturn2016 31.36%
2017 rr_AnnualReturn2017 13.13%
2018 rr_AnnualReturn2018 (13.96%)
2019 rr_AnnualReturn2019 26.16%
2020 rr_AnnualReturn2020 2.80%
2021 rr_AnnualReturn2021 29.49%
2022 rr_AnnualReturn2022 (11.12%)
2023 rr_AnnualReturn2023 10.86%
2024 rr_AnnualReturn2024 3.44%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 29.75%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (35.02%)
1 Year rr_AverageAnnualReturnYear01 3.44%
5 Years rr_AverageAnnualReturnYear05 6.29%
10 Years rr_AverageAnnualReturnYear10 7.80%
William Blair Small Cap Value Fund | Class R6  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Redemption Fee rr_RedemptionFeeOverRedemption none
Management Fee rr_ManagementFeesOverAssets 0.75%
Distribution (Rule 12b-1) Fee rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.04%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.79%
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets [1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 0.79%
1 Year rr_ExpenseExampleYear01 $ 81
3 Years rr_ExpenseExampleYear03 252
5 Years rr_ExpenseExampleYear05 439
10 Years rr_ExpenseExampleYear10 $ 978
1 Year rr_AverageAnnualReturnYear01 3.56%
Since Share Class Inception rr_AverageAnnualReturnSinceInception 3.12%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 19, 2021
William Blair Small Cap Value Fund | Return After Taxes on Distributions | Class I  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.45%
5 Years rr_AverageAnnualReturnYear05 4.72%
10 Years rr_AverageAnnualReturnYear10 5.91%
William Blair Small Cap Value Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class I  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.62%
5 Years rr_AverageAnnualReturnYear05 4.66%
10 Years rr_AverageAnnualReturnYear10 5.81%
William Blair Small Cap Value Fund | Russell 3000® Index (reflects no deduction for fees, expenses or taxes) | Class I  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 23.81%
5 Years rr_AverageAnnualReturnYear05 13.86%
10 Years rr_AverageAnnualReturnYear10 12.55%
William Blair Small Cap Value Fund | Russell 3000® Index (reflects no deduction for fees, expenses or taxes) | Class R6  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 23.81%
Since Share Class Inception rr_AverageAnnualReturnSinceInception 9.71%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 19, 2021
William Blair Small Cap Value Fund | Russell 2000® Value Index (reflects no deduction for fees, expenses or taxes) | Class I  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 8.05%
5 Years rr_AverageAnnualReturnYear05 7.29%
10 Years rr_AverageAnnualReturnYear10 7.14%
William Blair Small Cap Value Fund | Russell 2000® Value Index (reflects no deduction for fees, expenses or taxes) | Class R6  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 8.05%
Since Share Class Inception rr_AverageAnnualReturnSinceInception 3.81%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 19, 2021
[1]
William Blair Investment Management, LLC (the “Adviser”) has entered into a contractual agreement with the Fund to waive fees and/or reimburse expenses in order to limit the Fund’s operating expenses (excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of the Fund’s business) to 0.89% of average daily net assets for Class I shares until April 30, 2026. The Adviser may not terminate this arrangement prior to April 30, 2026 without the approval of the Fund’s Board of Trustees.