| Form N-CSR Cover | 6 Months Ended |
| Jun. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | William Blair Funds |
| Entity Central Index Key | 0000822632 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Shareholder Report | 6 Months Ended |
| Jun. 30, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | William Blair Funds |
| Entity Central Index Key | 0000822632 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| William Blair Growth Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Growth Fund |
| Class Name | Class I |
| Trading Symbol | BGFIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Growth Fund Class I $45 0.90% |
| Expenses Paid, Amount | $ 45 |
| Expense Ratio, Percent | 0.90% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 13.86% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 3000 ® ® Relative performance in the Fund was driven by a combination of stock-specific dynamics and style factors. From a sty le TOP PERFORMANCE CONTRIBUTORS Vital Farms Apple TOP PERFORMANCE DETRACTORS Five Below New Fortress Energy |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Growth Fund Class I 13.86% 24.73% 14.86% 13.31% S&P 500® Index 15.29% 24.56% 15.05% 12.86% Russell 3000® Growth Index 19.90% 32.22% 18.55% 15.75% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 261,353,000 |
| Holdings Count | Holding | 50 |
| Advisory Fees Paid, Amount | $ 651,000 |
| Investment Company, Portfolio Turnover | 31% |
| Additional Fund Statistics [Text Block] | Key Fu n Fund net assets (in $000s) $261,353 Number of portfolio holdings 50 Net advisory fees paid (in $000s) $651 Portfolio turnover rate (six months) 31% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Microsoft Corp. 8.8% Amazon.com, Inc. 8.0% Alphabet, Inc. 7.8% NVIDIA Corp. 4.8% Advanced Micro Devices, Inc. 4.1% Mastercard, Inc. 3.7% Apple, Inc. 3.5% UnitedHealth Group, Inc. 3.3% Palo Alto Networks, Inc. 3.2% ServiceNow, Inc. 3.2% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 8.8% Amazon.com, Inc. 8.0% Alphabet, Inc. 7.8% NVIDIA Corp. 4.8% Advanced Micro Devices, Inc. 4.1% Mastercard, Inc. 3.7% Apple, Inc. 3.5% UnitedHealth Group, Inc. 3.3% Palo Alto Networks, Inc. 3.2% ServiceNow, Inc. 3.2% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Growth Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Growth Fund |
| Class Name | Class N |
| Trading Symbol | WBGSX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Growth Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Growth Fund Class N $60 1.20% |
| Expenses Paid, Amount | $ 60 |
| Expense Ratio, Percent | 1.20% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 13.61% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 3000 ® ® Relative performance in the Fund was driven by a combination of cret TOP PERFORMANCE CONTRIBUTORS Vital Farms Apple TOP PERFORMANCE DETRACTORS Five Below New Fortress Energy |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $10,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Growth Fund Class N 13.61% 24.42% 14.54% 12.98% S&P 500® Index 15.29% 24.56% 15.05% 12.86% Russell 3000® Growth Index 19.90% 32.22% 18.55% 15.75% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 261,353,000 |
| Holdings Count | Holding | 50 |
| Advisory Fees Paid, Amount | $ 111,000 |
| Investment Company, Portfolio Turnover | 31% |
| Additional Fund Statistics [Text Block] | Key Fund S ti Fund net assets (in $000s) $261,353 Number of portfolio holdings 50 Net advisory fees paid (in $000s) $111 Portfolio turnover rate (six months) 31% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the in ve Top Ten Holdings Microsoft Corp. 8.8% Amazon.com, Inc. 8.0% Alphabet, Inc. 7.8% NVIDIA Corp. 4.8% Advanced Micro Devices, Inc. 4.1% Mastercard, Inc. 3.7% Apple, Inc. 3.5% UnitedHealth Group, Inc. 3.3% Palo Alto Networks, Inc. 3.2% ServiceNow, Inc. 3.2% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 8.8% Amazon.com, Inc. 8.0% Alphabet, Inc. 7.8% NVIDIA Corp. 4.8% Advanced Micro Devices, Inc. 4.1% Mastercard, Inc. 3.7% Apple, Inc. 3.5% UnitedHealth Group, Inc. 3.3% Palo Alto Networks, Inc. 3.2% ServiceNow, Inc. 3.2% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Debt Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsDebt Fund |
| Class Name | Class I |
| Trading Symbol | WEDIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Debt Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Debt Fund Class I $ 0.74% |
| Expenses Paid, Amount | $ 37 |
| Expense Ratio, Percent | 0.74% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.02% (net of fees) for the 6 months ended June 30, 2024 Positive contributions came from all three “beta buckets” (or risk categories), particularly the high-beta (higher-risk) bucket. For this group, positive performance was mainly the result of country allocation effects. Performance dium Higher-Risk Countries Within the higher-risk country segment, overweight positioning contributed the most to outperformance, especially in Egypt and Ecuador. Conversely, positions in Ethiopia and El Salvador detracted from relative performance. In Egypt, bond prices performed well as the government announced a significant foreign direct investment deal and secured an augmented financial arrangement with the International Monetary Fund (“IMF”). The devaluation of the Egyptian pound and significant tightening of monetary conditions further buoyed investor confidence. In Ecuador, bonds outperformed on an improving fundamental outlook for the country as well as an improvement in risk sentiment. Both country selection and security selection added to performance. Our small overweight position in Ethiopia detracted marginally from performance as the authorities failed to progress in negotiations with the IMF on a funded arrangement. In El Salvador, bonds lagged following the reelection of President Nayib Bukele. The market was expecting him to quickly turn to the IMF after his grasp on power was reaffirmed, but there continues to be an ideological conflict about the role bitcoin should have in the Salvadoran economy. An extended timeline and questions about the feasibility of an IMF program led bonds to underperform the Index. Lower-Risk Countries Within the lower-risk country segment, positions in Saudi Arabia and Indonesia contributed to performance. Conversely, positions in India and Paraguay detracted from performance. In Saudi Arabia, our underweight cash exposure position helped contribute to performance, which was aided by spread compression in our concentrated holdings in longer term bonds. In Indonesia, our underweight position in Indonesian sovereign spread duration and overweight position in an Indonesian corporate from the oil and gas sector contributed to the relative performance, as Indonesian sovereign spreads were already tight, so the country failed to take part in the rally of broader EM assets during the half of the year. In India, our off-benchmark position in short-dated corporate credit underperformed benchmark bonds as they failed to keep up with the very strong performance of the Index. Lastly, in Paraguay, our overweight position underperformed the Index, as many high-beta countries outperformed. Medium-Risk Countries Within the medium-risk country segment, positions in Turkey and South Africa contributed to relative performance. Conversely, positions in Uzbekistan and Guatemala detracted from relative performance. In Turkey, our position in a Turkish lira denominated supranational bond contributed to performance in the first half of 2024. In South Africa our underweight position contributed positively to performance as investors have become more nervous about the outcome of the election in May. Our overweight position in Uzbekistan detracted marginally to performance as a combination of a sovereign bond and a short-dated bank bond that we own failed to keep up with the very strong performance of the wider market. In Guatemala, our overweight in intermediate-term bonds detracted slightly from performance. Although the political environment in Guatemala improved markedly in January when President Bernardo Arévalo assumed office, the country’s performance to the Index lagged those of other medium-beta countries. |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Emerging Markets Debt Fund Class I 4.02% 12.20% (1.10)% Bloomberg Global Aggregate Index (3.16)% 0.93% (5.58)% JPMorgan Emerging Markets Bond Index (EMBI) Global Diversified (net) 2.34% 9.23% (2.22)% |
| Performance Inception Date | May 25, 2021 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 55,283,000 |
| Holdings Count | Holding | 245 |
| Advisory Fees Paid, Amount | $ 3,000 |
| Investment Company, Portfolio Turnover | 59% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $ Number of portfolio holdings 245 Net advisory fees paid (in $000s) $ Portfolio turnover rate (six months) 59% |
| Holdings [Text Block] | Graphical Representa t The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Credit quality designations range from AAA (highest) to D (lowest). Credit quality ratings on underlying securitie s are Top Ten Holdings Petroleos Mexicanos 3.0% Qatar Government International Bond 2.5% Romania Government International Bond 2.3% Panama Government International Bond 2.3% Argentine Government International Bond 2.3% Paraguay Government International Bond 2.2% South Africa Government International Bond 2.2% Oman Government International Bond 2.2% Turkiye Government International Bond 2.1% Dominican Republic 2.0 % Geographic Diversification Credit Quality |
| Largest Holdings [Text Block] | Top Ten Holdings Petroleos Mexicanos 3.0% Qatar Government International Bond 2.5% Romania Government International Bond 2.3% Panama Government International Bond 2.3% Argentine Government International Bond 2.3% Paraguay Government International Bond 2.2% South Africa Government International Bond 2.2% Oman Government International Bond 2.2% Turkiye Government International Bond 2.1% Dominican Republic 2.0 % |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Debt Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsDebt Fund |
| Class Name | Class R6 |
| Trading Symbol | WEDRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Debt Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Debt Fund Class R6 $ 0.69% |
| Expenses Paid, Amount | $ 35 |
| Expense Ratio, Percent | 0.69% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.05% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark Positive contributions came from all three “beta buckets” (or risk categories), particularly the high-beta (higher-risk) bucket. For this group, positive performance was mainly the result of country allocation effects. Performance in the medium-beta (medium-risk) and low-beta (lower-risk) bucket was driven predominantly by positive security-selection effects. Higher-Risk Countries Within the higher-risk country segment, overweight positioning contributed the most to outperformance, especially in Egypt and Ecuador. Conversely, positions in Ethiopia and El Salvador detracted from relative performance. In Egypt, bond prices performed well as the government announced a significant foreign direct investment deal and secured an augmented financial arrangement with the International Monetary Fund (“IMF”). The devaluation of the Egyptian pound and significant tightening of monetary conditions further buoyed investor confidence. In Ecuador, bonds outperformed on an improving fundamental outlook for the country as well as an improvement in risk sentiment. Both country selection and security selection added to performance. Our small overweight position in Ethiopia detracted marginally from performance as the authorities failed to progress in negotiations with the IMF on a funded arrangement. In El Salvador, bonds lagged following the reelection of President Nayib Bukele. The market was expecting him to quickly turn to the IMF after his grasp on power was reaffirmed, but there continues to be an ideological conflict about the role bitcoin should have in the Salvadoran economy. An extended timeline and questions about the feasibility of an IMF program led bonds to underperform the Index. Lower-Risk Countries Within the lower-risk country segment, positions in Saudi Arabia and Indonesia contributed to performance. Conversely, positions in India and Paraguay detracted from performance. In Saudi Arabia, our underweight cash exposure position helped contribute to performance, which was aided by spread compression in our concentrated holdings in longer term bonds. In Indonesia, our underweight position in Indonesian sovereign spread duration and overweight position in an Indonesian corporate from the oil and gas sector contributed to the relative performance, as Indonesian sovereign spreads were already tight, so the country failed to take part in the rally of broader EM assets during the half of the year. In India, our off-benchmark position in short-dated corporate credit underperformed benchmark bonds as they failed to keep up with the very strong performance of the Index. Lastly, in Paraguay, our overweight position underperformed the Index, as many high-beta countries outperformed. Medium-Risk Countries Within the medium-risk country segment, positions in Turkey and South Africa contributed to relative performance. Conversely, positions in Uzbekistan and Guatemala detracted from relative performance. In Turkey, our position in a Turkish lira denominated supranational bond contributed to performance in the first half of 2024. In South Africa our underweight position contributed positively to performance as investors have become more nervous about the outcome of the election in May. Our overweight position in Uzbekistan detracted marginally to performance as a combination of a sovereign bond and a short-dated bank bond that we own failed to keep up with the very strong performance of the wider market. In Guatemala, our overweight in intermediate-term bonds detracted slightly from performance. Although the political environment in Guatemala improved markedly in January when President Bernardo Arévalo assumed office, the co un |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Emerging Markets Debt Fund Class R6 4.05% 12.28% (1.05)% Bloomberg Global Aggregate Index (3.16)% 0.93% (5.58)% JPMorgan Emerging Markets Bond Index (EMBI) Global Diversified (net) 2.34% 9.23% (2.22)% |
| Performance Inception Date | May 25, 2021 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 55,283,000 |
| Holdings Count | Holding | 245 |
| Advisory Fees Paid, Amount | $ 66,000 |
| Investment Company, Portfolio Turnover | 59% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $55,283 Number of portfolio holdings 245 Net advisory fees paid (in $000s) $66 Portfolio turnover rate (six months) 59% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, repres en Fund on Top Ten Holdings Petroleos Mexicanos 3.0% Qatar Government International Bond 2.5% Romania Government International Bond 2.3% Panama Government International Bond 2.3% Argentine Government International Bond 2.3% Paraguay Government International Bond 2.2% South Africa Government International Bond 2.2% Oman Government International Bond 2.2% Turkiye Government International Bond 2.1% Dominican Republic 2.0 % Geographic Diversification Credit Quality |
| Largest Holdings [Text Block] | Top Ten Holdings Petroleos Mexicanos 3.0% Qatar Government International Bond 2.5% Romania Government International Bond 2.3% Panama Government International Bond 2.3% Argentine Government International Bond 2.3% Paraguay Government International Bond 2.2% South Africa Government International Bond 2.2% Oman Government International Bond 2.2% Turkiye Government International Bond 2.1% Dominican Republic 2.0 % |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Small Cap Growth Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsSmall Cap Growth Fund |
| Class Name | Class N |
| Trading Symbol | WESNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Small Cap Growth Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Small Cap Growth Fund Class N $70 1.40% |
| Expenses Paid, Amount | $ 70 |
| Expense Ratio, Percent | 1.40% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 10.22% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark, the MSCI Emerging Markets Small Cap Index (net), which returned 7.04% and outperformed the MSCI Emerging Markets IMI ( net Outperformance was driven by a combination of country allocation and stock selection effects. Stock selection was strong within the Industrials sector, particularly electrical equipment companies HD Hyundai Electric Co and ABB India. Within Materials, Jindal Stainless was a notable contributor to relative performance. The underweight to Health Care and Materials bolstered allocation effect. Pa r TOP PERFORMANCE CONTRIBUTORS HD Hyundai Electric Co Ltd ABB India e Jindal Stainless TOP PERFORMANCE DETRACTORS HPSP Global Unichip Totvs |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Small Cap Growth Fund Class N 10.22% 20.10% 10.23% 5.64% MSCI Emerging Markets IMI (net) 7.41% 13.56% 3.93% 3.09% MSCI Emerging Markets Small Cap Index (net) 7.04% 20.04% 9.99% 5.15% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 408,426,000 |
| Holdings Count | Holding | 130 |
| Advisory Fees Paid, Amount | $ 18,000 |
| Investment Company, Portfolio Turnover | 83% |
| Additional Fund Statistics [Text Block] | Fund net assets (in $000s) $408,426 Number of portfolio holdings 130 Net advisory fees paid (in $000s) $18 Portfolio turnover rate (six months) 83% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment m ak Top Ten Holdings Dixon Technologies India Ltd. 2.7% KEI Industries Ltd. 2.7% ABB India Ltd. 2.2% Wiwynn Corp. 2.1% ASPEED Technology, Inc. 2.0% Lotes Co. Ltd. 1.9% Asia Vital Components Co. Ltd. 1.8% Godrej Properties Ltd. 1.7% Huaming Power Equipment Co. Ltd. 1.6% Macrotech Developers Ltd. 1.6% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Dixon Technologies India Ltd. 2.7% KEI Industries Ltd. 2.7% ABB India Ltd. 2.2% Wiwynn Corp. 2.1% ASPEED Technology, Inc. 2.0% Lotes Co. Ltd. 1.9% Asia Vital Components Co. Ltd. 1.8% Godrej Properties Ltd. 1.7% Huaming Power Equipment Co. Ltd. 1.6% Macrotech Developers Ltd. 1.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsSmall Cap Growth Fund |
| Class Name | Class R6 |
| Trading Symbol | WESJX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Small Cap Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Small Cap Growth Fund Class R6 $55 1.10% |
| Expenses Paid, Amount | $ 55 |
| Expense Ratio, Percent | 1.10% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 10.34% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark, the MSCI Emerging Markets Small Cap Index (net), which returned 7.04% and outperformed the MSCI Emerging Markets IMI ( net TOP PERFORMANCE CONTRIBUTORS HD Hyundai Electric Co Ltd ABB India Jindal Stainless TOP PERFORMANCE DETRACTORS HPSP Global Unichip Totvs |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Small Cap Growth Fund Class R6 10.34% 20.42% 10.56% 6.00% MSCI Emerging Markets IMI (net) 7.41% 13.56% 3.93% 3.09% MSCI Emerging Markets Small Cap Index (net) 7.04% 20.04% 9.99% 5.15% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 408,426,000 |
| Holdings Count | Holding | 130 |
| Advisory Fees Paid, Amount | $ 1,106,000 |
| Investment Company, Portfolio Turnover | 83% |
| Additional Fund Statistics [Text Block] | Fund net assets (in $000s) $408,426 Number of portfolio holdings 130 Net advisory fees paid (in $000s) $1,106 Portfolio turnover rate (six months) 83% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund Top Ten Holdings Dixon Technologies India Ltd. 2.7% KEI Industries Ltd. 2.7% ABB India Ltd. 2.2% Wiwynn Corp. 2.1% ASPEED Technology, Inc. 2.0% Lotes Co. Ltd. 1.9% Asia Vital Components Co. Ltd. 1.8% Godrej Properties Ltd. 1.7% Huaming Power Equipment Co. Ltd. 1.6% Macrotech Developers Ltd. 1.6% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Dixon Technologies India Ltd. 2.7% KEI Industries Ltd. 2.7% ABB India Ltd. 2.2% Wiwynn Corp. 2.1% ASPEED Technology, Inc. 2.0% Lotes Co. Ltd. 1.9% Asia Vital Components Co. Ltd. 1.8% Godrej Properties Ltd. 1.7% Huaming Power Equipment Co. Ltd. 1.6% Macrotech Developers Ltd. 1.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair China Growth Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair China Growth Fund |
| Class Name | Class I |
| Trading Symbol | WICGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair China Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage China Growth Fund Class I $ 0.99% |
| Expenses Paid, Amount | $ 50 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 3.29% (net of fees) for the 6 months ended June 30 2024 Outperformance was driven by a combination of allocation and stock selection effects. An overweight allocation to Industrials as well as the stock selection within Consumer Discretionary and Consumer Staples were the primary drivers of outperformance. Partly offsetting these effects was the portfolio’s sector positioning, led by an overweight in Consumer Staples and underweight in Energy and Financials. Stock selection within Financials also hampered returns. TOP PERFORMANCE CONTRIBUTORS Hisense Home Appliances a Giant Biogene TOP PERFORMANCE DETRACTOR AIA Group |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception China Growth Fund Class I 3.29% (7.98)% (21.35)% MSCI China All Shares Index (net) 2.28% (4.39)% (13.18)% |
| Performance Inception Date | Aug. 27, 2021 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,815,000 |
| Holdings Count | Holding | 46 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 30% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $ Number of portfolio holdings 46 Net advisory fees paid (in $000s) $ Portfolio tu rnov 30% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Tencent Holdings Ltd. 11.3% NetEase, Inc. 6.3% Kweichow Moutai Co. Ltd. 5.1% PDD Holdings, Inc. 4.8% Huaneng Lancang River Hydropower, Inc. 4.5% NAURA Technology Group Co. Ltd. 4.1% Weichai Power Co. Ltd. 3.2% Contemporary Amperex Technology Co. Ltd. 2.9% Zhongji Innolight Co. Ltd. 2.6% Yutong Bus Co. Ltd. 2.6% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Tencent Holdings Ltd. 11.3% NetEase, Inc. 6.3% Kweichow Moutai Co. Ltd. 5.1% PDD Holdings, Inc. 4.8% Huaneng Lancang River Hydropower, Inc. 4.5% NAURA Technology Group Co. Ltd. 4.1% Weichai Power Co. Ltd. 3.2% Contemporary Amperex Technology Co. Ltd. 2.9% Zhongji Innolight Co. Ltd. 2.6% Yutong Bus Co. Ltd. 2.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair China Growth Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair China Growth Fund |
| Class Name | Class R6 |
| Trading Symbol | WRCGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair China Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage China Growth Fund Class R6 $ 0.94% |
| Expenses Paid, Amount | $ 47 |
| Expense Ratio, Percent | 0.94% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 3.30% (net of fees) for the 6 months ended June 30, 2024 Outperformance was driven by a combination of allocation and stock selection effects. An overweight allocation to Industrials as well as the stock selection within Consumer Discretionary and Consumer Staples were the primary drivers of outperformance. Partly offsetting these effects was the portfolio’s sector positioning, led by an overweight in Consumer Staples and und erw TOP PERFORMANCE CONTRIBUTORS Hisense Home Appliances -ba Giant Biogene TOP PERFORMANCE DETRACTOR AIA Group |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception China Growth Fund Class R6 3.30% (7.89)% (21.40)% MSCI China All Shares Index (net) 2.28% (4.39)% (13.18)% |
| Performance Inception Date | Aug. 27, 2021 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,815,000 |
| Holdings Count | Holding | 46 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 30% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,815 Number of portfolio holdings 46 Net advisory fees paid (in $000s) $0 Portfolio turnover rate (six months) 30% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing perce ntag Top Ten Holdings Tencent Holdings Ltd. 11.3% NetEase, Inc. 6.3% Kweichow Moutai Co. Ltd. 5.1% PDD Holdings, Inc. 4.8% Huaneng Lancang River Hydropower, Inc. 4.5% NAURA Technology Group Co. Ltd. 4.1% Weichai Power Co. Ltd. 3.2% Contemporary Amperex Technology Co. Ltd. 2.9% Zhongji Innolight Co. Ltd. 2.6% Yutong Bus Co. Ltd. 2.6% Sec t Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Tencent Holdings Ltd. 11.3% NetEase, Inc. 6.3% Kweichow Moutai Co. Ltd. 5.1% PDD Holdings, Inc. 4.8% Huaneng Lancang River Hydropower, Inc. 4.5% NAURA Technology Group Co. Ltd. 4.1% Weichai Power Co. Ltd. 3.2% Contemporary Amperex Technology Co. Ltd. 2.9% Zhongji Innolight Co. Ltd. 2.6% Yutong Bus Co. Ltd. 2.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Growth Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Growth Fund |
| Class Name | Class R6 |
| Trading Symbol | BGFRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Growth Fund Class R6 $43 0.86% |
| Expenses Paid, Amount | $ 43 |
| Expense Ratio, Percent | 0.86% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 13.87% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 3000 ® ® Relative performance in the Fund was driven by a combination of stock-specific dynamics and style factors. From a style perspective, our ty l Far TOP PERFORMANCE CONTRIBUTORS Vital Farms Apple TOP PERFORMANCE DETRACTORS Five Below New Fortress Energy |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $1,000,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years Since Inception Growth Fund Class R6 13.87% 24.79% 14.94% 14.99% S&P 500® Index 15.29% 24.56% 15.05% 14.76% Russell 3000® Growth Index 19.90% 32.22% 18.55% 18.09% |
| Performance Inception Date | May 02, 2019 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 261,353,000 |
| Holdings Count | Holding | 50 |
| Advisory Fees Paid, Amount | $ 176,000 |
| Investment Company, Portfolio Turnover | 31% |
| Additional Fund Statistics [Text Block] | Key Fun d Stat Fund net assets (in $000s) $261,353 Number of portfolio holdings 50 Net advisory fees paid (in $000s) $176 Portfolio turnover rate (six months) 31% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, re present Top Ten Holdings Microsoft Corp. 8.8% Amazon.com, Inc. 8.0% Alphabet, Inc. 7.8% NVIDIA Corp. 4.8% Advanced Micro Devices, Inc. 4.1% Mastercard, Inc. 3.7% Apple, Inc. 3.5% UnitedHealth Group, Inc. 3.3% Palo Alto Networks, Inc. 3.2% ServiceNow, Inc. 3.2% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 8.8% Amazon.com, Inc. 8.0% Alphabet, Inc. 7.8% NVIDIA Corp. 4.8% Advanced Micro Devices, Inc. 4.1% Mastercard, Inc. 3.7% Apple, Inc. 3.5% UnitedHealth Group, Inc. 3.3% Palo Alto Networks, Inc. 3.2% ServiceNow, Inc. 3.2% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Large Cap Growth Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Large Cap Growth Fund |
| Class Name | Class I |
| Trading Symbol | LCGFX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Large Cap Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Large Cap Growth Fund Class I $33 0.65 % |
| Expenses Paid, Amount | $ 33 |
| Expense Ratio, Percent | 0.65% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 20.50% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 1000 ® ® Relative performance drivers were largely stock-specific in nature. Top detractors in the Fund were Accenture (Information Technology), Monster Beverage Corp (Consumer Staples), Mastercard (Financials), and Salesforce (Information Technology), while not owning Meta (Communication Services) also dampened relative returns. Stock selection in Health Care, including our position in Zoetis and not owning Eli Lilly, further pressured performance versus the Index. Top contributors for the year-to-date period were NVIDIA (Information Technology), Lam Research (Information Technology) and Alphabet (Communication Services). Our underweight to Apple (Information Technology) was the largest contributor to relative -to TOP PERFORMANCE CONTRIBUTORS Apple NVIDIA TOP PERFORMANCE DETRACTORS Accenture Monster Beverage |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $500,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Large Cap Growth Fund Class I 20.50% 35.20% 17.08% 16.05% Russell 1000 ® 14.24% 23.88% 14.61% 12.51% Russell 1000 ® 20.70% 33.48% 19.34% 16.33% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 2,404,288,000 |
| Holdings Count | Holding | 31 |
| Advisory Fees Paid, Amount | $ 3,934,000 |
| Investment Company, Portfolio Turnover | 17% |
| Additional Fund Statistics [Text Block] | Key Fund St atis Fund net assets (in $000s) $2,404,288 Number of portfolio holdings 31 Net advisory fees paid (in $000s) $3,934 Portfolio turnover rate (six months) 17% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, rep re en Top Ten Holdings Microsoft Corp. 13.9% NVIDIA Corp. 10.7% Alphabet, Inc. 9.7% Amazon.com, Inc. 8.7% Apple, Inc. 6.3% Mastercard, Inc. 4.1% Intuit, Inc. 2.6% ServiceNow, Inc. 2.5% Lam Research Corp. 2.4% UnitedHealth Group, Inc. 2.4% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 13.9% NVIDIA Corp. 10.7% Alphabet, Inc. 9.7% Amazon.com, Inc. 8.7% Apple, Inc. 6.3% Mastercard, Inc. 4.1% Intuit, Inc. 2.6% ServiceNow, Inc. 2.5% Lam Research Corp. 2.4% UnitedHealth Group, Inc. 2.4% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Large Cap Growth Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Large Cap Growth Fund |
| Class Name | Class N |
| Trading Symbol | LCGNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Large Cap Growth Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Large Cap Growth Fund Class N $45 0.90 % |
| Expenses Paid, Amount | $ 45 |
| Expense Ratio, Percent | 0.90% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 20.31% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 1000 ® ® Relative performance drivers were largely stock-specific in nature. Top detractors in the Fund wer e Accent own TOP PERFORMANCE CONTRIBUTORS Apple NVIDIA TOP PERFORMANCE DETRACTORS Accenture Monster Beverage |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $10,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Large Cap Growth Fund Class N 20.31% 34.88% 16.78% 15.75% Russell 1000® Index 14.24% 23.88% 14.61% 12.51% Russell 1000® Growth Index 20.70% 33.48% 19.34% 16.33% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 2,404,288,000 |
| Holdings Count | Holding | 31 |
| Advisory Fees Paid, Amount | $ 418,000 |
| Investment Company, Portfolio Turnover | 17% |
| Additional Fund Statistics [Text Block] | Key Fund St Fund net assets (in $000s) $2,404,288 Number of portfolio holdings 31 Net advisory fees paid (in $000s) $418 Portfolio turnover rate (six months) 17% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representi ng perc Top Ten Holdings Microsoft Corp. 13.9% NVIDIA Corp. 10.7% Alphabet, Inc. 9.7% Amazon.com, Inc. 8.7% Apple, Inc. 6.3% Mastercard, Inc. 4.1% Intuit, Inc. 2.6% ServiceNow, Inc. 2.5% Lam Research Corp. 2.4% UnitedHealth Group, Inc. 2.4% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 13.9% NVIDIA Corp. 10.7% Alphabet, Inc. 9.7% Amazon.com, Inc. 8.7% Apple, Inc. 6.3% Mastercard, Inc. 4.1% Intuit, Inc. 2.6% ServiceNow, Inc. 2.5% Lam Research Corp. 2.4% UnitedHealth Group, Inc. 2.4% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Large Cap Growth Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Large Cap Growth Fund |
| Class Name | Class R6 |
| Trading Symbol | LCGJX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Large Cap Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Large Cap Growth Fund Class R6 $30 0.60 % |
| Expenses Paid, Amount | $ 30 |
| Expense Ratio, Percent | 0.60% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 20.50% (net of fees) for the 6 months ended June 3 0, 2 ts bench ® ® Relative performance drivers were largely stock-specific in nature. Top detractors in the Fund were Accenture (Information Technology), Monster Beverage Corp (Consumer Staples), Mastercard (Financials), and Salesforce (Information Technology), while not owning Meta (Communication Services) also dampened relative returns. Stock selection in Health Care, including our position in Zoetis and not owning Eli Lilly, further pressured performance versus the Index. Top contributors for the year-to-date period were NVIDIA (Information Technology), Lam Research (Information Technology) and Alphabet (Communication Services). Our underweight to Apple (Information Technology) was the largest contributor to relative returns year-to-date as the stock underperformed during the first quarter when we did not yet own it. Stock selection in Consumer Discretionary, including our position in Chipotle Mexican Grill and not owning Tesla, also benefitted relative performance. TOP PERFORMANCE CONTRIBUTORS Apple NVIDIA TOP PERFORMANCE DETRACTORS Accenture Monster Beverage |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $1,000,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years Since Inception Large Cap Growth Fund Class R6 20.50% 35.32% 17.13% 17.44% Russell 1000® Index 14.24% 23.88% 14.61% 14.31% Russell 1000® Growth Index 20.70% 33.48% 19.34% 18.86% |
| Performance Inception Date | May 02, 2019 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 2,404,288,000 |
| Holdings Count | Holding | 31 |
| Advisory Fees Paid, Amount | $ 1,168,000 |
| Investment Company, Portfolio Turnover | 17% |
| Additional Fund Statistics [Text Block] | Key Fund Sta ti Fund net assets (in $000s) $ Number of portfolio holdings 31 Net advisory fees paid (in $000s) $1,168 Portfolio turnover rate (six months) 17% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representin g p Top Ten Holdings Microsoft Corp. 13.9% NVIDIA Corp. 10.7% Alphabet, Inc. 9.7% Amazon.com, Inc. 8.7% Apple, Inc. 6.3% Mastercard, Inc. 4.1% Intuit, Inc. 2.6% ServiceNow, Inc. 2.5% Lam Research Corp. 2.4% UnitedHealth Group, Inc. 2.4% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 13.9% NVIDIA Corp. 10.7% Alphabet, Inc. 9.7% Amazon.com, Inc. 8.7% Apple, Inc. 6.3% Mastercard, Inc. 4.1% Intuit, Inc. 2.6% ServiceNow, Inc. 2.5% Lam Research Corp. 2.4% UnitedHealth Group, Inc. 2.4% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Mid Cap Value Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Mid Cap Value Fund |
| Class Name | Class I |
| Trading Symbol | WVMIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Mid Cap Value Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com. |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Mid Cap Value Fund Class I $38 0.76 % |
| Expenses Paid, Amount | $ 38 |
| Expense Ratio, Percent | 0.76% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 1.66% (net of fees) for the 6 months ended Jun e ® ® The Fund’s underperformance versus its benchmark was driven by negative stock selection in the Industrials, Materials, and Utilities sectors. While the Fund suffered from negative stock selection, the Fund was positively impacted due to a relative outperformance by the Fund’s holdings in the Financials, Consumer Staples, and Health Care sectors. TOP PERFORMANCE CONTRIBUTORS Flex Ralph Lauren Diamondback Energy TOP PERFORMANCE DETRACTORS Brunswick Envista Holdings Global Payments tio |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $500,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Mid Cap Value Fund Class I 1.66% 8.70% 2.94% Russell 3000® Index 13.56% 23.13% 12.09% Russell Midcap ® 4.54% 11.98% 4.52% |
| Performance Inception Date | Mar. 16, 2022 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,614,000 |
| Holdings Count | Holding | 59 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 26% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,614 Number of portfolio holdings 59 Net advisory fees paid (in $000s) $0 Portfolio turnover rate (six months) 26% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, represe Top Ten Holdings Qorvo, Inc. 2.1% Willis Towers Watson PLC 2.1% Ingredion, Inc. 2.1% Timken Co. 2.0% KKR & Co., Inc. 2.0% U.S. Foods Holding Corp. 1.9% Axalta Coating Systems Ltd. 1.9% NiSource, Inc. 1.9% Diamondback Energy, Inc. 1.9% Teleflex, Inc. 1.9% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Qorvo, Inc. 2.1% Willis Towers Watson PLC 2.1% Ingredion, Inc. 2.1% Timken Co. 2.0% KKR & Co., Inc. 2.0% U.S. Foods Holding Corp. 1.9% Axalta Coating Systems Ltd. 1.9% NiSource, Inc. 1.9% Diamondback Energy, Inc. 1.9% Teleflex, Inc. 1.9% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Mid Cap Value Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Mid Cap Value Fund |
| Class Name | Class R6 |
| Trading Symbol | WVMRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Mid Cap Value Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Mid Cap Value Fund Class R6 $ 0.70 % |
| Expenses Paid, Amount | $ 35 |
| Expense Ratio, Percent | 0.70% |
| Factors Affecting Performance [Text Block] | The Fund’s underperformance versus its benchmark was driven by negative stock selection in the Industrials, Materials, and Utilities sectors. While the Fund suffered from negative stock selection, the Fund was positively impacted due to a relative outperformance by the Fund’s holdings in the Financials, Consumer Staples, and Health Care sectors. TOP PERFORMANCE CONTRIBUTORS Flex Ralph Lauren Diamondback Energy TOP PERFORMANCE DETRACTORS Brunswick Envista Holdings Global Payments |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $1,000,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Mid Cap Value Fund Class R6 1.66% 8.75% 2.97% Russell 3000® Index 13.56% 23.13% 12.09% Russell Midcap® Value Index 4.54% 11.98% 4.52% |
| Performance Inception Date | Mar. 16, 2022 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,614,000 |
| Holdings Count | Holding | 59 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 26% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $ Number of portfolio holdings 59 Net advisory fees paid (in $000s) $0 Portfolio turnover rate (six months) 26% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of Top Ten Holdings Qorvo, Inc. 2.1% Willis Towers Watson PLC 2.1% Ingredion, Inc. 2.1% Timken Co. 2.0% KKR & Co., Inc. 2.0% U.S. Foods Holding Corp. 1.9% Axalta Coating Systems Ltd. 1.9% NiSource, Inc. 1.9% Diamondback Energy, Inc. 1.9% Teleflex, Inc. 1.9% |
| Largest Holdings [Text Block] | Top Ten Holdings Qorvo, Inc. 2.1% Willis Towers Watson PLC 2.1% Ingredion, Inc. 2.1% Timken Co. 2.0% KKR & Co., Inc. 2.0% U.S. Foods Holding Corp. 1.9% Axalta Coating Systems Ltd. 1.9% NiSource, Inc. 1.9% Diamondback Energy, Inc. 1.9% Teleflex, Inc. 1.9% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small-Mid Cap Core Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small-Mid CapCore Fund |
| Class Name | Class I |
| Trading Symbol | WBCIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small-Mid Cap Core Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the l as (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small-Mid Cap Core Fund Class I $ 0.95% |
| Expenses Paid, Amount | $ 48 |
| Expense Ratio, Percent | 0.95% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 0.07% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 2500™ Index, which returned 2.35% and underperformed the Russell 3000 ® Relative performance of the Fund was driven by stock specific dynamics. From a sector perspective, stock selection within Energy, including our position in New Fortress Energy, and Health Care, detracted from relative performance. TOP PERFORMANCE CONTRIBUTORS Baldwin Insurance Primo Water TOP PERFORMANCE DETRACTORS New Fortress Energy Mercury Systems |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $500,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Small-Mid Cap Core Fund Class I 0.07% 4.88% 9.41% Russell 3000® Index 13.56% 23.13% 14.65% Russell 2500™ Index 2.35% 10.47% 9.06% |
| Performance Inception Date | Oct. 01, 2019 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 197,484,000 |
| Holdings Count | Holding | 88 |
| Advisory Fees Paid, Amount | $ 374,000 |
| Investment Company, Portfolio Turnover | 29% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $ Number of portfolio holdings 88 Net advisory fees paid (in $000s) $374 Portfolio turnover rate (six months) 29% |
| Holdings [Text Block] | Graphical Representation of H olding The tables below show the investment makeup of the Fund, representing percentage of th e tota Top Ten Holdings BWX Technologies, Inc. 2.4% Baldwin Insurance Group, Inc. 2.3% Everest Group Ltd. 2.1% Western Alliance Bancorp 2.0% Bright Horizons Family Solutions, Inc. 1.9% Carlyle Group, Inc. 1.9% Casella Waste Systems, Inc. 1.9% Garrett Motion, Inc. 1.7% East West Bancorp, Inc. 1.7% ACV Auctions, Inc. 1.6% |
| Largest Holdings [Text Block] | Top Ten Holdings BWX Technologies, Inc. 2.4% Baldwin Insurance Group, Inc. 2.3% Everest Group Ltd. 2.1% Western Alliance Bancorp 2.0% Bright Horizons Family Solutions, Inc. 1.9% Carlyle Group, Inc. 1.9% Casella Waste Systems, Inc. 1.9% Garrett Motion, Inc. 1.7% East West Bancorp, Inc. 1.7% ACV Auctions, Inc. 1.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| Small-Mid Cap Core Fund Class R6 [Member] | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small-Mid CapCore Fund |
| Class Name | Class R6 |
| Trading Symbol | WBCRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small-Mid Cap Core Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small-Mid Cap Core Fund Class R6 $ 0.90% |
| Expenses Paid, Amount | $ 45 |
| Expense Ratio, Percent | 0.90% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 0.13% (net of fees) for the 6 mon th ® Relative performance of the Fund was driven by stock specific dynamics. From a sector perspective, stock selection within Energy, including our position in New Fortress Energy, and Health Care, detracted from relative performance. TOP PERFORMANCE CONTRIBUTORS Baldwin Insurance Primo Water TOP PERFORMANCE DETRACTORS New Fortress Energy Mercury Systems |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $1,000,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Small-Mid Cap Core Fund Class R6 0.13% 4.92% 9.46% Russell 3000® Index 13.56% 23.13% 14.65% Russell 2500™ Index 2.35% 10.47% 9.06% |
| Performance Inception Date | Oct. 01, 2019 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 197,484,000 |
| Holdings Count | Holding | 88 |
| Advisory Fees Paid, Amount | $ 374,000 |
| Investment Company, Portfolio Turnover | 29% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $ Number of portfolio holdings 88 Net advisory fees paid (in $000s) $374 Portfolio turnover rate (six months) 29% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment ma keup o Top Ten Holdings BWX Technologies, Inc. 2.4% Baldwin Insurance Group, Inc. 2.3% Everest Group Ltd. 2.1% Western Alliance Bancorp 2.0% Bright Horizons Family Solutions, Inc. 1.9% Carlyle Group, Inc. 1.9% Casella Waste Systems, Inc. 1.9% Garrett Motion, Inc. 1.7% East West Bancorp, Inc. 1.7% ACV Auctions, Inc. 1.6% |
| Largest Holdings [Text Block] | Top Ten Holdings BWX Technologies, Inc. 2.4% Baldwin Insurance Group, Inc. 2.3% Everest Group Ltd. 2.1% Western Alliance Bancorp 2.0% Bright Horizons Family Solutions, Inc. 1.9% Carlyle Group, Inc. 1.9% Casella Waste Systems, Inc. 1.9% Garrett Motion, Inc. 1.7% East West Bancorp, Inc. 1.7% ACV Auctions, Inc. 1.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small-Mid CapGrowth Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small-Mid CapGrowth Fund |
| Class Name | Class I |
| Trading Symbol | WSMDX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small-Mid Cap Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small-Mid Cap Growth Fund Class I $ 0.99% |
| Expenses Paid, Amount | $ 50 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 1.34% (net of fees) for the 6 months ended June 30, 2024. The Fund underperfo rm ® Relative performance of the Fund was driven by stock specific dynamics. From a sector perspective, stock selection in Energy, including our position in New Fortress Energy, and Health Care, including our position in Evolent Health, detracted from relative performance. Other individual detractors included Five Below (Consumer Discretionary), Shoals Technologies Group (Industrials) and Mercury Systems (Industrials). Not owning Microstrategy (Information Technology) and Deckers (Consumer Discretionary) also detracted from relative performance. Positive stock selection in Consumer Staples, including our positions in Freshpet and e.l.f. Beauty, contributed to relative performance. Other top individual contributors included Insmed (Health Care), Super Micro Computer (Information Technology) and Encompass Health (Health Care). TOP PERFORMANCE CONTRIBUTORS Freshpet e.l.f. Beauty TOP PERFORMANCE DETRACTORS New Fortress Energy Five Below |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Small-Mid Cap Growth Fund Class I 1.34% 6.89% 6.82% 10.01% Russell 3000® Index 13.56% 23.13% 14.14% 12.15% Russell 2500™ Growth Index 3.93% 9.02% 7.58% 8.77% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,864,134,000 |
| Holdings Count | Holding | 77 |
| Advisory Fees Paid, Amount | $ 5,621,000 |
| Investment Company, Portfolio Turnover | 24% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,864,134 Number of portfolio holdings 77 Net advisory fees paid (in $000s) $5,621 Portfolio turnover rate (six months) 24% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the F und percentage Top Ten Holdings BWX Technologies, Inc. 2.6% e.l.f. Beauty, Inc. 2.5% Encompass Health Corp. 2.4% Freshpet, Inc. 2.2% Carlyle Group, Inc. 2.1% Chemed Corp. 2.1% Advanced Drainage Systems, Inc. 2.0% Tyler Technologies, Inc. 1.9% Brink's Co. 1.8% Axon Enterprise, Inc. 1.8% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings BWX Technologies, Inc. 2.6% e.l.f. Beauty, Inc. 2.5% Encompass Health Corp. 2.4% Freshpet, Inc. 2.2% Carlyle Group, Inc. 2.1% Chemed Corp. 2.1% Advanced Drainage Systems, Inc. 2.0% Tyler Technologies, Inc. 1.9% Brink's Co. 1.8% Axon Enterprise, Inc. 1.8% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small-Mid CapGrowth Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small-Mid CapGrowth Fund |
| Class Name | Class N |
| Trading Symbol | WSMNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small-Mid Cap Growth Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information abo ut www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small-Mid Cap Growth Fund Class N $ 1.24% |
| Expenses Paid, Amount | $ 62 |
| Expense Ratio, Percent | 1.24% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 1.20% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 2500™ Growth Index, which returned 3.93% and underperformed the Russell 3000 ® Relative performance of the Fund was driven by stock specific dynamics. From a sector perspective, stock selection in Energy, including our position in New Fortress Energy, and Health Care, including our position in Evolent Health, detracted from relative performance. Other individual detractors included Five Below (Consumer Discretionary), Shoals Technologies Group (Industrials) and Mercury Systems (Industrials). Not owning Microstrategy (Information Technology) and Deckers (Consumer Discretionary) also detracted from relative performance. Positive stock selection in Consumer Staples, including our positions in Freshpet and e.l.f. Beauty, contributed to relative performance. Other top individual contributors included Insmed (Health Care), Super Micro Computer (Information Technology) and Encompass Health (Health Care). TOP PERFORMANCE CONTRIBUTORS Freshpet company e.l.f. Beauty TOP PERFORMANCE DETRACTORS New Fortress Energy Five Below |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Small-Mid Cap Growth Fund Class N 1.20% 6.63% 6.55% 9.72% Russell 3000® Index 13.56% 23.13% 14.14% 12.15% Russell 2500™ Growth Index 3.93% 9.02% 7.58% 8.77% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,864,134,000 |
| Holdings Count | Holding | 77 |
| Advisory Fees Paid, Amount | $ 409,000 |
| Investment Company, Portfolio Turnover | 24% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $ Number of portfolio holdings 77 Net advisory fees paid (in $000s) $ Portfolio turnover rate (six months) 24% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings BWX Technologies, Inc. 2.6% e.l.f. Beauty, Inc. 2.5% Encompass Health Corp. 2.4% Freshpet, Inc. 2.2% Carlyle Group, Inc. 2.1% Chemed Corp. 2.1% Advanced Drainage Systems, Inc. 2.0% Tyler Technologies, Inc. 1.9% Brink's Co. 1.8% Axon Enterprise, Inc. 1.8% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings BWX Technologies, Inc. 2.6% e.l.f. Beauty, Inc. 2.5% Encompass Health Corp. 2.4% Freshpet, Inc. 2.2% Carlyle Group, Inc. 2.1% Chemed Corp. 2.1% Advanced Drainage Systems, Inc. 2.0% Tyler Technologies, Inc. 1.9% Brink's Co. 1.8% Axon Enterprise, Inc. 1.8% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small-Mid Cap Growth Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small-Mid CapGrowth Fund |
| Class Name | Class R6 |
| Trading Symbol | WSMRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small-Mid Cap Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small-Mid Cap Growth Fund Class R6 $ 0.94% |
| Expenses Paid, Amount | $ 47 |
| Expense Ratio, Percent | 0.94% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 1.34% (net of fees) for the 6 months ended Jun e 3 ® Relative performance of the Fund was driven by stock specific dynamics. From a sector perspective, stock selection in Energy, including our position in New Fortress Energy, and Health Care, including our position in Evolent Health, detracted from relative performance. Other individual detractors included Five Below (Consumer Discretionary), Shoals Technologies Group (Industrials) and Mercury Systems (Industrials). Not owning Microstrategy (Information Technology) and Deckers (Consumer Discretionary) also detracted from relative performance. Positive stock selection in Consumer Staples, including our positions in Freshpet and e.l.f. Beauty, contributed to relative performance. Other top individual contributors included Insmed (Health Care), Super Micro Computer (Information Technology) and Encompass Health (Health Care). TOP PERFORMANCE CONTRIBUTORS Freshpet e.l.f. Beauty TOP PERFORMANCE DETRACTORS New Fortress Energy Five Below |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years Since Inception Small-Mid Cap Growth Fund Class R6 1.34% 6.90% 6.87% 7.24% Russell 3000® Index 13.56% 23.13% 14.14% 13.84% Russell 2500™ Growth Index 3.93% 9.02% 7.58% 7.70% |
| Performance Inception Date | May 02, 2019 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,864,134,000 |
| Holdings Count | Holding | 77 |
| Advisory Fees Paid, Amount | $ 1,941,000 |
| Investment Company, Portfolio Turnover | 24% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,864,134 Number of portfolio holdings 77 Net advisory fees paid (in $000s) $1,941 Portfolio turnover rate (six months) 24% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings BWX Technologies, Inc. 2.6% e.l.f. Beauty, Inc. 2.5% Encompass Health Corp. 2.4% Freshpet, Inc. 2.2% Carlyle Group, Inc. 2.1% Chemed Corp. 2.1% Advanced Drainage Systems, Inc. 2.0% Tyler Technologies, Inc. 1.9% Brink's Co. 1.8% Axon Enterprise, Inc. 1.8% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings BWX Technologies, Inc. 2.6% e.l.f. Beauty, Inc. 2.5% Encompass Health Corp. 2.4% Freshpet, Inc. 2.2% Carlyle Group, Inc. 2.1% Chemed Corp. 2.1% Advanced Drainage Systems, Inc. 2.0% Tyler Technologies, Inc. 1.9% Brink's Co. 1.8% Axon Enterprise, Inc. 1.8% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small-Mid CapValue Fund |
| Class Name | Class I |
| Trading Symbol | ISMVX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small-Mid Cap Value Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small-Mid Cap Value Fund Class I $43 0.85% |
| Expenses Paid, Amount | $ 43 |
| Expense Ratio, Percent | 0.85% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned -0.75% (net of fees) for the 6 months ended June 30, 2024 ® ® The Fund’s underperformance versus its benchmark was primarily driven by poor stock selection in the Consumer Discretionary, Materials, and Industrials sectors. Despite negative performance, the Fund had a positive all oc TOP PERFORMANCE CONTRIBUTORS Expro’s Ralph Lauren Encompass Health TOP PERFORMANCE DETRACTORS QuidelOrtho Bloomin’ Brands Cracker Barrel Old Country Store |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months Since Inception Small-Mid Cap Value Fund Class I (0.75)% 5.65% Russell 3000® Index 13.56% 25.21% Russell 2500 ® 1.50% 12.22% |
| Performance Inception Date | Aug. 17, 2023 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 2,690,000,000 |
| Holdings Count | Holding | 86 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 29% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund $2,690 Number of portfolio holdings 86 Net advisory fees paid (in $000s) $0 Portfolio turnover rate (six months) 29% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing net Top Ten Holdings Taylor Morrison Home Corp. 1.6% ABM Industries, Inc. 1.6% Qorvo, Inc. 1.5% Ingredion, Inc. 1.5% Commercial Metals Co. 1.5% Tecnoglass, Inc. 1.5% Healthpeak Properties, Inc. 1.4% Avnet, Inc. 1.4% SM Energy Co. 1.4% U.S. Foods Holding Corp. 1.4% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Taylor Morrison Home Corp. 1.6% ABM Industries, Inc. 1.6% Qorvo, Inc. 1.5% Ingredion, Inc. 1.5% Commercial Metals Co. 1.5% Tecnoglass, Inc. 1.5% Healthpeak Properties, Inc. 1.4% Avnet, Inc. 1.4% SM Energy Co. 1.4% U.S. Foods Holding Corp. 1.4% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small-Mid CapValue Fund |
| Class Name | Class R6 |
| Trading Symbol | RSMVX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small-Mid Cap Value Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small-Mid Cap Value Fund Class R6 $40 0.80% |
| Expenses Paid, Amount | $ 40 |
| Expense Ratio, Percent | 0.80% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned -0.75% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its be nch ® ® The Fund’s underperformance versus its benchmark was primarily driven by poor stock selection in the Consumer Discretionary, Materials, and Industrials sectors. Despite negative performance, the Fund had a positive allocation effect in 9 of the 11 Global Industry Classification Standard economic sectors during the period. Specifically, the Fund benefited from an overweight position to the Industrials and Information Technology sectors and an underweight position to the Financials and Communications Services sectors. TOP PERFORMANCE CONTRIBUTORS Expro’s Ralph Lauren Encompass Health TOP PERFORMANCE DETRACTORS QuidelOrtho Bloomin’ Brands Cracker Barrel Old Country Store |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months Since Inception Small-Mid Cap Value Fund Class R6 (0.75)% 5.70% Russell 3000® Index 13.56% 25.21% Russell 2500® Value Index 1.50% 12.22% |
| Performance Inception Date | Aug. 17, 2023 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 2,690,000 |
| Holdings Count | Holding | 86 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 29% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $2,690 Number of portfolio holdings 86 Net advisory fees paid (in $000s) $0 Portfolio turnover rate (six months) 29% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage Top Ten Holdings Taylor Morrison Home Corp. 1.6% ABM Industries, Inc. 1.6% Qorvo, Inc. 1.5% Ingredion, Inc. 1.5% Commercial Metals Co. 1.5% Tecnoglass, Inc. 1.5% Healthpeak Properties, Inc. 1.4% Avnet, Inc. 1.4% SM Energy Co. 1.4% U.S. Foods Holding Corp. 1.4% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Taylor Morrison Home Corp. 1.6% ABM Industries, Inc. 1.6% Qorvo, Inc. 1.5% Ingredion, Inc. 1.5% Commercial Metals Co. 1.5% Tecnoglass, Inc. 1.5% Healthpeak Properties, Inc. 1.4% Avnet, Inc. 1.4% SM Energy Co. 1.4% U.S. Foods Holding Corp. 1.4% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| C000023541 [Member] | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small Cap Growth Fund |
| Class Name | Class I |
| Trading Symbol | WBSIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small Cap Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblair funds |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small Cap Growth Fund Class I $50 0.99% |
| Expenses Paid, Amount | $ 50 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 7.84% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark, the Russell 2000 ® ® Outperformance was attributable to stock specific dynamics. The portfolio benefited from strong selection in Consumer Staples, including our positions in Vital Farms and e.l.f. Beauty, and Health Care, including our positions in Insmed and Encompass Health. Our position in Sylvamo (Materials) also contributed positively to performance. Top detractors year-to-date included New Fortress Energy (Energy), Inspire Medical (Health Care) Amicus Therapeutics (Health Care) and Treace Medical Concepts (Health Care). Industrials stock selection, including our position in Shoals Technologies Group, as well as not owning MicroStrategy (Information Technology), dampened relative results. From a style perspective, stocks with strong price momentum generally outperformed in the period which was a modest headwind to relative performance given our typical below-benchmark exposure to momentum. TOP PERFORMANCE CONTRIBUTORS Vital Farms reported Insmed TOP PERFORMANCE DETRACTORS New Fortress Energy Shoals Technologies |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Small Cap Growth Fund Class I 7.84% 12.73% 9.76% 10.61% Russell 3000® Index 13.56% 23.13% 14.14% 12.15% Russell 2000® Growth Index 4.44% 9.14% 6.17% 7.39% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 822,617,000 |
| Holdings Count | Holding | 91 |
| Advisory Fees Paid, Amount | $ 1,860,000 |
| Investment Company, Portfolio Turnover | 29% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $822,617 Number of portfolio holdings 91 Net advisory fees paid (in $000s) $1,860 Portfolio turnover rate (six months) 29% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total Top Ten Holdings Casella Waste Systems, Inc. 2.2% Brink's Co. 2.1% BWX Technologies, Inc. 2.1% Insmed, Inc. 1.9% Verra Mobility Corp. 1.8% Encompass Health Corp. 1.7% e.l.f. Beauty, Inc. 1.6% Guidewire Software, Inc. 1.6% Skyline Champion Corp. 1.6% Baldwin Insurance Group, Inc. 1.6% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Casella Waste Systems, Inc. 2.2% Brink's Co. 2.1% BWX Technologies, Inc. 2.1% Insmed, Inc. 1.9% Verra Mobility Corp. 1.8% Encompass Health Corp. 1.7% e.l.f. Beauty, Inc. 1.6% Guidewire Software, Inc. 1.6% Skyline Champion Corp. 1.6% Baldwin Insurance Group, Inc. 1.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small Cap Growth Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small Cap Growth Fund |
| Class Name | Class N |
| Trading Symbol | WBSNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small Cap Growth Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small Cap Growth Fund Class N $62 1.24% |
| Expenses Paid, Amount | $ 62 |
| Expense Ratio, Percent | 1.24% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 7.71% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark, the Russell 2000 ® ® market Outperformance was attributable to stock specific dynamics. The portfolio benefited from strong selection in Consumer Staples, including our positions in Vital Farms and e.l.f. Beauty, and Health Care, including our positions in Insmed and Encompass Health. Our position in Sylvamo (Materials) also contributed positively to performance. Top detractors year-to-date included New Fortress Energy (Energy), Inspire Medical (Health Care) Amicus Therapeutics (Health Care) and Treace Medical Concepts (Health Care). Industrials stock selection, including our position in Shoals Technologies Group, as well as not owning MicroStrategy (Information Technology), dampened relative results. From a style perspective, stocks with strong price momentum generally outperformed in the period which was a modest headwind to relative performance given our typical below-benchmark exposure to momentum. TOP PERFORMANCE CONTRIBUTORS Vital Farms egg Insmed TOP PERFORMANCE DETRACTORS New Fortress Energy Shoals Technologies |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Small Cap Growth Fund Class N 7.71% 12.46% 9.48% 10.34% Russell 3000® Index 13.56% 23.13% 14.14% 12.15% Russell 2000® Growth Index 4.44% 9.14% 6.17% 7.39% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 822,617,000 |
| Holdings Count | Holding | 91 |
| Advisory Fees Paid, Amount | $ 491,000 |
| Investment Company, Portfolio Turnover | 29% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $822,617 Number of portfolio holdings 91 Net advisory fees paid (in $000s) $491 Portfolio turnover rate (six months) 29% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage Top Ten Holdings Casella Waste Systems, Inc. 2.2% Brink's Co. 2.1% BWX Technologies, Inc. 2.1% Insmed, Inc. 1.9% Verra Mobility Corp. 1.8% Encompass Health Corp. 1.7% e.l.f. Beauty, Inc. 1.6% Guidewire Software, Inc. 1.6% Skyline Champion Corp. 1.6% Baldwin Insurance Group, Inc. 1.6% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Casella Waste Systems, Inc. 2.2% Brink's Co. 2.1% BWX Technologies, Inc. 2.1% Insmed, Inc. 1.9% Verra Mobility Corp. 1.8% Encompass Health Corp. 1.7% e.l.f. Beauty, Inc. 1.6% Guidewire Software, Inc. 1.6% Skyline Champion Corp. 1.6% Baldwin Insurance Group, Inc. 1.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small Cap Growth Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small Cap Growth Fund |
| Class Name | Class R6 |
| Trading Symbol | WBSRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small Cap Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small Cap Growth Fund Class R6 $47 0.94% |
| Expenses Paid, Amount | $ 47 |
| Expense Ratio, Percent | 0.94% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 7.88% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark, the Russell 2000 ® ® Outperformance was attributable to stock specific dynamics. The portfolio benefited from strong selection in Consumer Staples, including our positions in Vital Farms and e.l.f. Beauty, and Health Care, including our positions in Insmed and Encompass Health. Our position in Sylvamo (Materials) also contributed positively to performance. Top detractors year-to-date included New Fortress Energy (Energy), Inspire Medical (Health Care) Amicus Therapeutics (Health Care) and Treace Medical Concepts (Health Care). Industrials stoc TOP PERFORMANCE CONTRIBUTORS Vital Farms expected Insmed TOP PERFORMANCE DETRACTORS New Fortress Energy Shoals Technologies |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years Since Inception Small Cap Growth Fund Class R6 7.88% 12.82% 9.83% 9.47% Russell 3000® Index 13.56% 23.13% 14.14% 13.84% Russell 2000® Growth Index 4.44% 9.14% 6.17% 6.12% |
| Performance Inception Date | May 02, 2019 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 822,617,000 |
| Holdings Count | Holding | 91 |
| Advisory Fees Paid, Amount | $ 851,000 |
| Investment Company, Portfolio Turnover | 29% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $822,617 Number of portfolio holdings 91 Net advisory fees paid (in $000s) $851 Portfolio turnover rate (six months) 29% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Casella Waste Systems, Inc. 2.2% Brink's Co. 2.1% BWX Technologies, Inc. 2.1% Insmed, Inc. 1.9% Verra Mobility Corp. 1.8% Encompass Health Corp. 1.7% e.l.f. Beauty, Inc. 1.6% Guidewire Software, Inc. 1.6% Skyline Champion Corp. 1.6% Baldwin Insurance Group, Inc. 1.6% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Casella Waste Systems, Inc. 2.2% Brink's Co. 2.1% BWX Technologies, Inc. 2.1% Insmed, Inc. 1.9% Verra Mobility Corp. 1.8% Encompass Health Corp. 1.7% e.l.f. Beauty, Inc. 1.6% Guidewire Software, Inc. 1.6% Skyline Champion Corp. 1.6% Baldwin Insurance Group, Inc. 1.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small Cap Value Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small Cap Value Fund |
| Class Name | Class I |
| Trading Symbol | ICSCX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small Cap Value Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small Cap Value Fund Class I $45 0.89% |
| Expenses Paid, Amount | $ 45 |
| Expense Ratio, Percent | 0.89% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned -1.95% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 2000 ® ® et The Fund’s underperformance versus its benchmark was driven by poor stock selection in the Consumer Discretionary, Materials, and Industrials sectors. Despite negative performance, the Fund had positive stock selection in 7 of the 11 Global Industry Classification Standard economic sectors during the period. The Fund’s sector allocations were additive to relative performance primarily due to an underweight TOP PERFORMANCE CONTRIBUTORS Expro’s Tower Semiconductor Granite Construction TOP PERFORMANCE DETRACTORS Ryerson Holding Titan Machinery Bloomin’ Brands |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Small Cap Value Fund Class I (1.95)% 6.54% 6.69% 7.11% Russell 3000® Index 13.56% 23.13% 14.14% 12.15% Russell 2000 ® (0.85)% 10.90% 7.07% 6.23% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,315,970,000 |
| Holdings Count | Holding | 110 |
| Advisory Fees Paid, Amount | $ 2,961,000 |
| Investment Company, Portfolio Turnover | 13% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,315,970 Number of portfolio holdings 110 Net advisory fees paid (in $000s) $2,961 Portfolio turnover rate (six months) 13% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Expro Group Holdings NV 1.5% Verint Systems, Inc. 1.4% Kite Realty Group Trust 1.3% Taylor Morrison Home Corp. 1.3% SM Energy Co. 1.3% Granite Construction, Inc. 1.3% John Wiley & Sons, Inc. 1.3% Tri Pointe Homes, Inc. 1.3% ABM Industries, Inc. 1.3% Cal-Maine Foods, Inc. 1.2% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Expro Group Holdings NV 1.5% Verint Systems, Inc. 1.4% Kite Realty Group Trust 1.3% Taylor Morrison Home Corp. 1.3% SM Energy Co. 1.3% Granite Construction, Inc. 1.3% John Wiley & Sons, Inc. 1.3% Tri Pointe Homes, Inc. 1.3% ABM Industries, Inc. 1.3% Cal-Maine Foods, Inc. 1.2% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small Cap Value Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small Cap Value Fund |
| Class Name | Class N |
| Trading Symbol | WBVNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small Cap Value Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small Cap Value Fund Class N $58 1.15% |
| Expenses Paid, Amount | $ 58 |
| Expense Ratio, Percent | 1.15% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned -2.05% (net of fees) for the 6 months ended June 30, 2024. The Fund u nde ® ® 13.56 The Fund’s underperformance versus its benchmark was driven by poor stock selection in the Consumer Discretionary, Materials, and Industrials sectors. Despite negative performance, the Fund had positive stock selection in 7 of the 11 Global Industry Classification Standard economic sectors during the period. The Fund’s sector allocations were additive to relative performance primarily due to an underweight position to the Financials sector and an overweight position to the Industrials sector TOP PERFORMANCE CONTRIBUTORS Expro’s Tower Semiconductor Granite Construction TOP PERFORMANCE DETRACTORS Ryerson Holding Titan Machinery icultu Bloomin’ Brands |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Small Cap Value Fund Class N (2.05)% 6.29% 1.43% Russell 3000® Index 13.56% 23.13% 8.25% Russell 2000® Value Index (0.85)% 10.90% 1.47% |
| Performance Inception Date | Jul. 17, 2021 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,315,970,000 |
| Holdings Count | Holding | 110 |
| Advisory Fees Paid, Amount | $ 9,000 |
| Investment Company, Portfolio Turnover | 13% |
| Additional Fund Statistics [Text Block] | Fund net assets (in $000s) $1,315,970 Number of portfolio holdings 110 Net advisory fees paid (in $000s) $9 Portfolio turnover rate (six months) 13% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of of Top Ten Holdings Expro Group Holdings NV 1.5% Verint Systems, Inc. 1.4% Kite Realty Group Trust 1.3% Taylor Morrison Home Corp. 1.3% SM Energy Co. 1.3% Granite Construction, Inc. 1.3% John Wiley & Sons, Inc. 1.3% Tri Pointe Homes, Inc. 1.3% ABM Industries, Inc. 1.3% Cal-Maine Foods, Inc. 1.2% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Expro Group Holdings NV 1.5% Verint Systems, Inc. 1.4% Kite Realty Group Trust 1.3% Taylor Morrison Home Corp. 1.3% SM Energy Co. 1.3% Granite Construction, Inc. 1.3% John Wiley & Sons, Inc. 1.3% Tri Pointe Homes, Inc. 1.3% ABM Industries, Inc. 1.3% Cal-Maine Foods, Inc. 1.2% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Small Cap Value Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Small Cap Value Fund |
| Class Name | Class R6 |
| Trading Symbol | WBVRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Small Cap Value Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Small Cap Value Fund Class R6 $40 0.79% |
| Expenses Paid, Amount | $ 40 |
| Expense Ratio, Percent | 0.79% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned -1.88% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the Russell 2000 ® ® 13.56 The Fund’s underperformance versus its benchmark was driven by poor stock selection in the Co nsu TOP PERFORMANCE CONTRIBUTORS Expro’s Tower Semiconductor Granite Construction TOP PERFORMANCE DETRACTORS Ryerson Holding Titan Machinery Bloomin’ Brands |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Small Cap Value Fund Class R6 (1.88)% 6.64% 1.78% Russell 3000 ® 13.56 % 23.13 % 8.25 % Russell 2000 ® (0.85 ) % 10.90 % 1.47 % |
| Performance Inception Date | Jul. 17, 2021 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,315,970,000 |
| Holdings Count | Holding | 110 |
| Advisory Fees Paid, Amount | $ 1,861,000 |
| Investment Company, Portfolio Turnover | 13% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,315,970 Number of portfolio holdings 110 Net advisory fees paid (in $000s) $1,861 Portfolio turnover rate (six months) 13% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Expro Group Holdings NV 1.5% Verint Systems, Inc. 1.4% Kite Realty Group Trust 1.3% Taylor Morrison Home Corp. 1.3% SM Energy Co. 1.3% Granite Construction, Inc. 1.3% John Wiley & Sons, Inc. 1.3% Tri Pointe Homes, Inc. 1.3% ABM Industries, Inc. 1.3% Cal-Maine Foods, Inc. 1.2% Sector Allocation |
| Largest Holdings [Text Block] | Top Ten Holdings Expro Group Holdings NV 1.5% Verint Systems, Inc. 1.4% Kite Realty Group Trust 1.3% Taylor Morrison Home Corp. 1.3% SM Energy Co. 1.3% Granite Construction, Inc. 1.3% John Wiley & Sons, Inc. 1.3% Tri Pointe Homes, Inc. 1.3% ABM Industries, Inc. 1.3% Cal-Maine Foods, Inc. 1.2% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Global Leaders Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Global Leaders Fund |
| Class Name | Class I |
| Trading Symbol | WGFIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Global Leaders Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Global Leaders Fund Class I $ 0.90% |
| Expenses Paid, Amount | $ 45 |
| Expense Ratio, Percent | 0.90% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 8.06% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI All Country World IMI (net), which returned 10.28%. The Fund's benchmark is also a broad measure of market performance. Relative underperformance was driven by stock selection across sectors and in the United States. Selection in Information Technology (“IT”), Industrials, and Financials were the primary detractors. While the overweight to IT was additive, negative selection was driven by an underweight position in NVIDIA as it was purchased late in the quarter. Within Industrials, Airbus and Old Dominion Freight Line were the primary detractors, while AIA weighed on Financials returns. Partly offsetting underperformance was a combination of sector allocation driven by an overweight to IT and underweight to Consumer Staples and stock selection in Communication Services. Within IT, the overweight to a strong sector and selection outside of the U.S. including positions in TSMC and MediaTek were both additive. TOP PERFORMANCE CONTRIBUTORS TSMC e MediaTek Meta Platforms TOP PERFORMANCE DETRACTORS Airbus Old Dominion AIA Group |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Global Leaders Fund Class I 8.06% 12.08% 9.57% 9.00% MSCI All Country World IMI (net) 10.28% 18.40% 10.36% 8.17% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 103,624,000 |
| Holdings Count | Holding | 68 |
| Advisory Fees Paid, Amount | $ 245,000 |
| Investment Company, Portfolio Turnover | 22% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $ Number of portfolio holdings 68 Net advisory fees paid (in $000s) $245 Portfolio turnover rate (six months) 22% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total of the Top Ten Holdings Microsoft Corp. 6.6% Taiwan Semiconductor Manufacturing Co. Ltd. 4.4% Alphabet, Inc. 4.4% Amazon.com, Inc. 3.5% Mastercard, Inc. 3.2% Novo Nordisk AS 3.2% NVIDIA Corp. 3.1% Meta Platforms, Inc. 2.7% Atlas Copco AB 2.1% ASML Holding NV 2.1% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 6.6% Taiwan Semiconductor Manufacturing Co. Ltd. 4.4% Alphabet, Inc. 4.4% Amazon.com, Inc. 3.5% Mastercard, Inc. 3.2% Novo Nordisk AS 3.2% NVIDIA Corp. 3.1% Meta Platforms, Inc. 2.7% Atlas Copco AB 2.1% ASML Holding NV 2.1% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Global Leaders Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Global Leaders Fund |
| Class Name | Class N |
| Trading Symbol | WGGNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Global Leaders Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Global Leaders Fund Class N $58 1.15% |
| Expenses Paid, Amount | $ 58 |
| Expense Ratio, Percent | 1.15% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 7.96% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI All Country World IMI (net), which returned 10.28%. The Fund's benchmark is also a broad measure of market performance. Relative underperformance was driven by stock selection across sectors and in the United States. Selection in Information Technology (“IT”), Industrials, and Financials were the primary detractors. While the overweight to I T TOP PERFORMANCE CONTRIBUTORS TSMC MediaTek Meta Platforms TOP PERFORMANCE DETRACTORS Airbus Old Dominion AIA Group |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Global Leaders Fund Class N 7.96% 11.75% 9.31% 8.71% MSCI All Country World IMI (net) 10.28% 18.40% 10.36% 8.17% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 103,624,000 |
| Holdings Count | Holding | 68 |
| Advisory Fees Paid, Amount | $ 25,000 |
| Investment Company, Portfolio Turnover | 22% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $103,624 Number of portfolio holdings 68 Net advisory fees paid (in $000s) $25 Portfolio turnover rate (six months) 22% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Microsoft Corp. 6.6% Taiwan Semiconductor Manufacturing Co. Ltd. 4.4% Alphabet, Inc. 4.4% Amazon.com, Inc. 3.5% Mastercard, Inc. 3.2% Novo Nordisk AS 3.2% NVIDIA Corp. 3.1% Meta Platforms, Inc. 2.7% Atlas Copco AB 2.1% ASML Holding NV 2.1% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 6.6% Taiwan Semiconductor Manufacturing Co. Ltd. 4.4% Alphabet, Inc. 4.4% Amazon.com, Inc. 3.5% Mastercard, Inc. 3.2% Novo Nordisk AS 3.2% NVIDIA Corp. 3.1% Meta Platforms, Inc. 2.7% Atlas Copco AB 2.1% ASML Holding NV 2.1% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Global Leaders Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Global Leaders Fund |
| Class Name | Class R6 |
| Trading Symbol | BGGIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Global Leaders Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Global Leaders Fund Class R6 $43 0.85% |
| Expenses Paid, Amount | $ 43 |
| Expense Ratio, Percent | 0.85% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 8.06% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI All Country World IMI (net), which returned 10.28%. The Fund's benchmark is also a broad measure of market performance. ele TOP PERFORMANCE CONTRIBUTORS TSMC MediaTek Meta Platforms TOP PERFORMANCE DETRACTORS Airbus Old Dominion AIA Group |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Global Leaders Fund Class R6 8.06% 12.06% 9.63% 9.05% MSCI All Country World IMI (net) 10.28% 18.40% 10.36% 8.17% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 103,624,000 |
| Holdings Count | Holding | 68 |
| Advisory Fees Paid, Amount | $ 50,000 |
| Investment Company, Portfolio Turnover | 22% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $103,624 Number of portfolio holdings 68 Net advisory fees paid (in $000s) $50 Portfolio turnover rate (six months) 22% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Microsoft Corp. 6.6% Taiwan Semiconductor Manufacturing Co. Ltd. 4.4% Alphabet, Inc. 4.4% Amazon.com, Inc. 3.5% Mastercard, Inc. 3.2% Novo Nordisk AS 3.2% NVIDIA Corp. 3.1% Meta Platforms, Inc. 2.7% Atlas Copco AB 2.1% ASML Holding NV 2.1% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Microsoft Corp. 6.6% Taiwan Semiconductor Manufacturing Co. Ltd. 4.4% Alphabet, Inc. 4.4% Amazon.com, Inc. 3.5% Mastercard, Inc. 3.2% Novo Nordisk AS 3.2% NVIDIA Corp. 3.1% Meta Platforms, Inc. 2.7% Atlas Copco AB 2.1% ASML Holding NV 2.1% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Leaders Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalLeaders Fund |
| Class Name | Class I |
| Trading Symbol | WILIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Leaders Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Leaders Fund Class I $45 0.90% |
| Expenses Paid, Amount | $ 45 |
| Expense Ratio, Percent | 0.90% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 5.97% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark, the MSCI All Country World ex-U.S. IMI (net), which returned 5.28%. The Fund's benchmark is also a broad measure of market performance. Outperformance was primarily driven by allocation effect, with an overweight to Information Technology, where the semiconductor industry has been notably strong, and underweights to Real Estate and Consumer Staples adding value, while an underweight to Financials detracted. Selection effect was negative primarily within Financials and Consumer Discretionary. This was partly offset by p osit TOP PERFORMANCE CONTRIBUTOR Novo Nordisk HDFC Bank lululemon |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years International Leaders Fund Class I 5.97% 7.38% 5.48% 6.23% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,172,797,000 |
| Holdings Count | Holding | 64 |
| Advisory Fees Paid, Amount | $ 1,715,000 |
| Investment Company, Portfolio Turnover | 27% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,172,797 Number of portfolio holdings 64 Net advisory fees paid (in $000s) $1,715 Portfolio turnover rate (six months) 27% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 4.8% ASML Holding NV 4.0% Novo Nordisk AS 3.7% Tokyo Electron Ltd. 2.4% MediaTek, Inc. 2.4% Reliance Industries Ltd. 2.3% ICON PLC 2.3% Atlas Copco AB 2.2% London Stock Exchange Group PLC 2.1% Hoya Corp. 2.1% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 4.8% ASML Holding NV 4.0% Novo Nordisk AS 3.7% Tokyo Electron Ltd. 2.4% MediaTek, Inc. 2.4% Reliance Industries Ltd. 2.3% ICON PLC 2.3% Atlas Copco AB 2.2% London Stock Exchange Group PLC 2.1% Hoya Corp. 2.1% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Leaders Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalLeaders Fund |
| Class Name | Class N |
| Trading Symbol | WILNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Leaders Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Leaders Fund Class N $58 1.15% |
| Expenses Paid, Amount | $ 58 |
| Expense Ratio, Percent | 1.15% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 5.81% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark, the MSCI All Country World ex- U.S Outperformance was primarily driven by allocation eff e notably HDFC Bank lululemon Fund Performance The following graph compares the initial and subsequent account values for the 10-year period ended June 30, 2024 |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $10,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years International Leaders Fund Class N 5.81% 7.11% 5.22% 5.97% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,172,797,000 |
| Holdings Count | Holding | 64 |
| Advisory Fees Paid, Amount | $ 124,000 |
| Investment Company, Portfolio Turnover | 27% |
| Additional Fund Statistics [Text Block] | Fund net assets (in $000s) $1,172,797 Number of portfolio holdings 64 Net advisory fees paid (in $000s) $124 Portfolio turnover rate (six months) 27% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 4.8% ASML Holding NV 4.0% Novo Nordisk AS 3.7% Tokyo Electron Ltd. 2.4% MediaTek, Inc. 2.4% Reliance Industries Ltd. 2.3% ICON PLC 2.3% Atlas Copco AB 2.2% London Stock Exchange Group PLC 2.1% Hoya Corp. 2.1% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 4.8% ASML Holding NV 4.0% Novo Nordisk AS 3.7% Tokyo Electron Ltd. 2.4% MediaTek, Inc. 2.4% Reliance Industries Ltd. 2.3% ICON PLC 2.3% Atlas Copco AB 2.2% London Stock Exchange Group PLC 2.1% Hoya Corp. 2.1% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Leaders Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalLeaders Fund |
| Class Name | Class R6 |
| Trading Symbol | WILJX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Leaders Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Leaders Fund Class R6 $43 0.85% |
| Expenses Paid, Amount | $ 43 |
| Expense Ratio, Percent | 0.85% |
| Factors Affecting Performance [Text Block] | Outperformance was primarily driven by allocation effect, with an overweight to Information Technology, whe r HDFC Bank lululemon Fund Performance The following graph compares the initial and subsequent account values for the 10-year period ended June 30, 2024 (or for the life of the Fund, if shorter). It assumes a $1,000,000 initial investment at the beginning of the period in a broad-based securities market index which is also generally representative of the market sectors or types of investments in which the Fund invests. |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $1,000,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years International Leaders Fund Class R6 5.96% 7.43% 5.54% 6.31% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,172,797,000 |
| Holdings Count | Holding | 64 |
| Advisory Fees Paid, Amount | $ 2,416,000 |
| Investment Company, Portfolio Turnover | 27% |
| Additional Fund Statistics [Text Block] | Fund net assets (in $000s) $1,172,797 Number of portfolio holdings 64 Net advisory fees paid (in $000s) $2,416 Portfolio turnover rate (six months) 27% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 4.8% ASML Holding NV 4.0% Novo Nordisk AS 3.7% Tokyo Electron Ltd. 2.4% MediaTek, Inc. 2.4% Reliance Industries Ltd. 2.3% ICON PLC 2.3% Atlas Copco AB 2.2% London Stock Exchange Group PLC 2.1% Hoya Corp. 2.1% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 4.8% ASML Holding NV 4.0% Novo Nordisk AS 3.7% Tokyo Electron Ltd. 2.4% MediaTek, Inc. 2.4% Reliance Industries Ltd. 2.3% ICON PLC 2.3% Atlas Copco AB 2.2% London Stock Exchange Group PLC 2.1% Hoya Corp. 2.1% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Growth Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalGrowth Fund |
| Class Name | Class I |
| Trading Symbol | BIGIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Growth Fund Class I $50 0.99% |
| Expenses Paid, Amount | $ 50 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.60% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark Selection effect was negative primarily within Industrials and Information Technology (“IT”). This was partly offset by positive selection within Health Care. Allocation effect was positive driven by overweight exposure to IT and underweight exposure to the Materials and Real Estate sectors. TOP PERFORMANCE CONTRIBUTOR Novo Nordisk TOP PERFORMANCE DETRACTORS Ryanair ad Vinci DSV |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years International Growth Fund Class I 4.60% 8.48% 6.37% 4.74% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,475,594,000 |
| Holdings Count | Holding | 169 |
| Advisory Fees Paid, Amount | $ 4,237,000 |
| Investment Company, Portfolio Turnover | 18% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,475,594 Number of portfolio holdings 169 Net advisory fees paid (in $000s) $4,237 Portfolio turnover rate (six months) 18% |
| Holdings [Text Block] | Graphical Representation The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 3.6% Novo Nordisk AS 2.6% ASML Holding NV 2.6% Samsung Electronics Co. Ltd. 1.5% London Stock Exchange Group PLC 1.4% 3i Group PLC 1.4% Reliance Industries Ltd. 1.4% Keyence Corp. 1.3% Tokio Marine Holdings, Inc. 1.3% SAP SE 1.3% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 3.6% Novo Nordisk AS 2.6% ASML Holding NV 2.6% Samsung Electronics Co. Ltd. 1.5% London Stock Exchange Group PLC 1.4% 3i Group PLC 1.4% Reliance Industries Ltd. 1.4% Keyence Corp. 1.3% Tokio Marine Holdings, Inc. 1.3% SAP SE 1.3% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Growth Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalGrowth Fund |
| Class Name | Class N |
| Trading Symbol | WBIGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Growth Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Growth Fund Class N $ 1.24% |
| Expenses Paid, Amount | $ 62 |
| Expense Ratio, Percent | 1.24% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.47% (net of fees) for the 6 months ended June 30, 2024. The Selection effect was negative primarily within Industrials and Information Technology (“IT”). This was partly offset by positive selection within Health Care. Allocation effect was positive driven by overweight exposure to IT and underweight exposure to the Materials and Real Estate sectors. TOP PERFORMANCE CONTRIBUTOR Novo Nordisk market ght TOP PERFORMANCE DETRACTORS Ryanair Vinci DSV |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years International Growth Fund Class N 4.47% 8.23% 6.08% 4.44% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,475,594,000 |
| Holdings Count | Holding | 169 |
| Advisory Fees Paid, Amount | $ 1,144,000 |
| Investment Company, Portfolio Turnover | 18% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,475,594 Number of portfolio holdings 169 Net advisory fees paid (in $000s) $1,144 Portfolio turnover rate (six months) 18% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 3.6% Novo Nordisk AS 2.6% ASML Holding NV 2.6% Samsung Electronics Co. Ltd. 1.5% London Stock Exchange Group PLC 1.4% 3i Group PLC 1.4% Reliance Industries Ltd. 1.4% Keyence Corp. 1.3% Tokio Marine Holdings, Inc. 1.3% SAP SE 1.3% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 3.6% Novo Nordisk AS 2.6% ASML Holding NV 2.6% Samsung Electronics Co. Ltd. 1.5% London Stock Exchange Group PLC 1.4% 3i Group PLC 1.4% Reliance Industries Ltd. 1.4% Keyence Corp. 1.3% Tokio Marine Holdings, Inc. 1.3% SAP SE 1.3% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Growth Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalGrowth Fund |
| Class Name | Class R6 |
| Trading Symbol | WBIRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Growth Fund Class R6 $ 0.94% |
| Expenses Paid, Amount | $ 47 |
| Expense Ratio, Percent | 0.94% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.60% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI All Country World ex-U.S. IMI (net), which returned 5.28%. The Fund's benchmark is also a broad measure of market performance. Selection effect was negative primarily within Industrials and Information Technology (“IT”). This was partly offset by positive selection within Health Care. Allocation effect was positive driven by overweight exposure to IT and underweight exposure to the Materials and Real Estate sectors. TOP PERFORMANCE CONTRIBUTOR Novo Nordisk currently TOP PERFORMANCE DETRACTORS Ryanair o Vinci DSV |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years Since Inception International Growth Fund Class R6 4.60% 8.52% 6.44% 6.65% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 5.43% |
| Performance Inception Date | May 02, 2019 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 1,475,594,000 |
| Holdings Count | Holding | 169 |
| Advisory Fees Paid, Amount | $ 646,000 |
| Investment Company, Portfolio Turnover | 18% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $1,475,594 Number of portfolio holdings 169 Net advisory fees paid (in $000s) $646 Portfolio turnover rate (six months) 18% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 3.6% Novo Nordisk AS 2.6% ASML Holding NV 2.6% Samsung Electronics Co. Ltd. 1.5% London Stock Exchange Group PLC 1.4% 3i Group PLC 1.4% Reliance Industries Ltd. 1.4% Keyence Corp. 1.3% Tokio Marine Holdings, Inc. 1.3% SAP SE 1.3% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 3.6% Novo Nordisk AS 2.6% ASML Holding NV 2.6% Samsung Electronics Co. Ltd. 1.5% London Stock Exchange Group PLC 1.4% 3i Group PLC 1.4% Reliance Industries Ltd. 1.4% Keyence Corp. 1.3% Tokio Marine Holdings, Inc. 1.3% SAP SE 1.3% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Institutional International Growth Fund Institutional Class | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InstitutionalInternational Growth Fund |
| Class Name | Institutional Class |
| Trading Symbol | WBIIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Institutional International Growth Fund Institutional Class (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Institutional International Growth Fund $47 0.94% |
| Expenses Paid, Amount | $ 47 |
| Expense Ratio, Percent | 0.94% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.58% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI All Country World ex-U.S. IMI (net), which returned 5.28%. The Fund's benchmark is also a broad measure of market performance. Selection effect was negative primarily within Industrials and Information Technology (“IT”). This was partly offset by positive selection within Health Care. Allocation effect was positive driven by overweight exposure to IT and underweight exposure TOP PERFORMANCE CONTRIBUTOR Novo Nordisk gs cu TOP PERFORMANCE DETRACTORS Ryanair Vinci DSV |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Institutional International Growth Fund 4.58% 8.24% 6.51% 4.88% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 972,862,000 |
| Holdings Count | Holding | 169 |
| Advisory Fees Paid, Amount | $ 4,173,000 |
| Investment Company, Portfolio Turnover | 19% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $972,862 Number 169 Net advisory fees paid (in $000s) $4,173 Portfolio turnover rate (six months) 19% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 3.6% Novo Nordisk AS 2.7% ASML Holding NV 2.6% Samsung Electronics Co. Ltd. 1.5% London Stock Exchange Group PLC 1.4% 3i Group PLC 1.4% Reliance Industries Ltd. 1.4% Keyence Corp. 1.3% Tokio Marine Holdings, Inc. 1.3% SAP SE 1.3% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 3.6% Novo Nordisk AS 2.7% ASML Holding NV 2.6% Samsung Electronics Co. Ltd. 1.5% London Stock Exchange Group PLC 1.4% 3i Group PLC 1.4% Reliance Industries Ltd. 1.4% Keyence Corp. 1.3% Tokio Marine Holdings, Inc. 1.3% SAP SE 1.3% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Small Cap Growth Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalSmall Cap Growth Fund |
| Class Name | Class I |
| Trading Symbol | WISIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Small Cap Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Small Cap Growth Fund Class I $55 1.10% |
| Expenses Paid, Amount | $ 55 |
| Expense Ratio, Percent | 1.10% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned -2.10% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI All Country World ex-U.S. Small Cap Index (net), which returned 2.78% and underperformed the MSCI All Country World ex-U.S. IMI (net), a broad measure of market performance, which returned 5.28%. Japan positioning and stock selection has hampered relative performance, particularly our exposure to domestic-oriented, higher-value, human-capital-intensive business models. These companies have been punished offset TOP PERFORMANCE CONTRIBUTORS Pro Medicus CTS Eventim TOP PERFORMANCE DETRACTORS Technopro SHIFT |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years International Small Cap Growth Fund Class I (2.10)% 3.20% 3.39% 3.00% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% MSCI All Country World ex-U.S. Small Cap Index (net) 2.78% 11.26% 6.13% 4.44% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 191,737,000 |
| Holdings Count | Holding | 113 |
| Advisory Fees Paid, Amount | $ 421,000 |
| Investment Company, Portfolio Turnover | 23% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $191,737 Number of portfolio holdings 113 Net advisory fees paid (in $000s) $421 Portfolio turnover rate (six months) 23% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Pro Medicus Ltd. 2.6% Diploma PLC 2.2% North West Co., Inc. 2.0% Beazley PLC 2.0% Lifco AB 1.9% Beijer Ref AB 1.9% ASPEED Technology, Inc. 1.8% Hemnet Group AB 1.8% CTS Eventim AG & Co. KGaA 1.8% D'ieteren Group 1.7% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Pro Medicus Ltd. 2.6% Diploma PLC 2.2% North West Co., Inc. 2.0% Beazley PLC 2.0% Lifco AB 1.9% Beijer Ref AB 1.9% ASPEED Technology, Inc. 1.8% Hemnet Group AB 1.8% CTS Eventim AG & Co. KGaA 1.8% D'ieteren Group 1.7% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Small Cap Growth Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalSmall Cap Growth Fund |
| Class Name | Class N |
| Trading Symbol | WISNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Small Cap Growth Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Small Cap Growth Fund Class N $68 1.35% |
| Expenses Paid, Amount | $ 68 |
| Expense Ratio, Percent | 1.35% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned -2.21% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI All Country World ex-U.S. Small Cap Index (net), which returned Japan positioning and stock selection has hampered relative performance, particularly our exposure to domestic-oriented, higher-value, human-capital-intensive business models. These companies have been punished more recently by wage inflation and a significant weakening in the yen. Underperformance has been driven by weaker stock selection within Japan Industrials and Information TOP PERFORMANCE CONTRIBUTORS Pro Medicus n t CTS Eventim TOP PERFORMANCE DETRACTORS Technopro SHIFT |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years International Small Cap Growth Fund Class N (2.21)% 2.97% 3.13% 2.72% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% MSCI All Country World ex-U.S. Small Cap Index (net) 2.78% 11.26% 6.13% 4.44% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 191,737,000 |
| Holdings Count | Holding | 113 |
| Advisory Fees Paid, Amount | $ 6,000 |
| Investment Company, Portfolio Turnover | 23% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $191,737 Number of portfolio holdings 113 Net advisory fees paid $6 Portfolio turnover rate (six months) 23% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Pro Medicus Ltd. 2.6% Diploma PLC 2.2% North West Co., Inc. 2.0% Beazley PLC 2.0% Lifco AB 1.9% Beijer Ref AB 1.9% ASPEED Technology, Inc. 1.8% Hemnet Group AB 1.8% CTS Eventim AG & Co. KGaA 1.8% D'ieteren Group 1.7% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Pro Medicus Ltd. 2.6% Diploma PLC 2.2% North West Co., Inc. 2.0% Beazley PLC 2.0% Lifco AB 1.9% Beijer Ref AB 1.9% ASPEED Technology, Inc. 1.8% Hemnet Group AB 1.8% CTS Eventim AG & Co. KGaA 1.8% D'ieteren Group 1.7% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair International Small Cap Growth Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair InternationalSmall Cap Growth Fund |
| Class Name | Class R6 |
| Trading Symbol | WIISX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair International Small Cap Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage International Small Cap Growth Fund Class R6 $53 1.05% |
| Expenses Paid, Amount | $ 53 |
| Expense Ratio, Percent | 1.05% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned -2.09% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its b ench Japan positioning and stock selection has hampered relative performance, particularly our exposure to domestic-oriented, higher-value, human-capital-intensive business models. These companies have been punished more recently by wage inflation and a significant weakening in the yen. Underperformance has been driven by weaker stock selection within Japan Industrials and Information Technology (“IT”), which more than offset positive stock selection within Health Care, Communication Services and Consumer Staples. CTS Eventim level SHIFT |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years International Small Cap Growth Fund Class R6 (2.09)% 3.24% 3.49% 3.09% MSCI All Country World ex-U.S. IMI (net) 5.28% 11.57% 5.62% 3.92% MSCI All Country World ex-U.S. Small Cap Index (net) 2.78% 11.26% 6.13% 4.44% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 191,737,000 |
| Holdings Count | Holding | 113 |
| Advisory Fees Paid, Amount | $ 582,000 |
| Investment Company, Portfolio Turnover | 23% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $191,737 Number of portfolio holdings 113 Net advisory fees paid (in $000s) $582 Portfolio turnover rate (six months) 23% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Pro Medicus Ltd. 2.6% Diploma PLC 2.2% North West Co., Inc. 2.0% Beazley PLC 2.0% Lifco AB 1.9% Beijer Ref AB 1.9% ASPEED Technology, Inc. 1.8% Hemnet Group AB 1.8% CTS Eventim AG & Co. KGaA 1.8% D'ieteren Group 1.7% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Pro Medicus Ltd. 2.6% Diploma PLC 2.2% North West Co., Inc. 2.0% Beazley PLC 2.0% Lifco AB 1.9% Beijer Ref AB 1.9% ASPEED Technology, Inc. 1.8% Hemnet Group AB 1.8% CTS Eventim AG & Co. KGaA 1.8% D'ieteren Group 1.7% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Leaders Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsLeaders Fund |
| Class Name | Class I |
| Trading Symbol | WBELX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Leaders Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Leaders Fund Class I $50 0.99% |
| Expenses Paid, Amount | $ 50 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.45% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI Emerging Markets Index (net), which returned 7.49%. The Fund's benchmark is also a broad measure of market performance. The underperformance was driven by a combination of an overweight to Latin America and stock selection within the Financials and Information Technology (“IT”) sectors. Within Financials, HDFC and BTG Pactual were notable detractors to relative results, while Globant and Totvs were meaningful detractors in IT. Partly offsetting these effects were positive sector allocation led by an overweight to IT and specifically IT hardware including SK Hynix and MediaTek, and an underweight to Materials, as well as stock selection within the Consumer Discre tio Mahindra & Mahindra BTG Pactual Totvs Globant |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Leaders Fund Class I 4.45% 5.89% 1.26% 2.06% MSCI Emerging Markets Index (net) 7.49% 12.55% 3.10% 2.79% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 203,619,000 |
| Holdings Count | Holding | 62 |
| Advisory Fees Paid, Amount | $ 47,000 |
| Investment Company, Portfolio Turnover | 35% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $203,619 Number of portfolio holdings 62 Net advisory fees paid (in $000s) $47 Portfolio turnover rate (six months) 35% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.0% Samsung Electronics Co. Ltd. 7.8% Tencent Holdings Ltd. 5.3% MediaTek, Inc. 3.5% Kotak Mahindra Bank Ltd. 3.0% Reliance Industries Ltd. 3.0% WEG SA 2.8% SK Hynix, Inc. 2.7% MercadoLibre, Inc. 2.6% Bank Central Asia Tbk. PT 2.5% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.0% Samsung Electronics Co. Ltd. 7.8% Tencent Holdings Ltd. 5.3% MediaTek, Inc. 3.5% Kotak Mahindra Bank Ltd. 3.0% Reliance Industries Ltd. 3.0% WEG SA 2.8% SK Hynix, Inc. 2.7% MercadoLibre, Inc. 2.6% Bank Central Asia Tbk. PT 2.5% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Leaders Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsLeaders Fund |
| Class Name | Class N |
| Trading Symbol | WELNX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Leaders Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Leaders Fund Class N $62 1.24% |
| Expenses Paid, Amount | $ 62 |
| Expense Ratio, Percent | 1.24% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.47% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI Emerging Markets Index (net), which returned 7.49%. The Fund's benchmark is also a broad measure of market performance. The underperformance was driven by a combination of an overweight to Latin America and stock selection within the Financials and Information Technology (“IT”) sectors. Within Financials, HDFC and BTG Pactual were notable detractors to relative results, while Globant and Totvs were meaningful detractors in IT. Partly offsetting these effects were positive sector allocation led by an overweight to IT and specifically IT hardware including SK Hynix and MediaTek, and an underweight to Materials, as well as stock selection within the Consumer Discretionary sector. Mahindra & Mahindra BTG Pactual Totvs Globant |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Leaders Fund Class N 4.47% 5.61% 1.03% 1.79% MSCI Emerging Markets Index (net) 7.49% 12.55% 3.10% 2.79% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 203,619,000 |
| Holdings Count | Holding | 62 |
| Advisory Fees Paid, Amount | $ 4,000 |
| Investment Company, Portfolio Turnover | 35% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $203,619 Number of portfolio holdings 62 Net advisory fees paid (in $000s) $4 Portfolio turnover rate (six months) 35% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.0% Samsung Electronics Co. Ltd. 7.8% Tencent Holdings Ltd. 5.3% MediaTek, Inc. 3.5% Kotak Mahindra Bank Ltd. 3.0% Reliance Industries Ltd. 3.0% WEG SA 2.8% SK Hynix, Inc. 2.7% MercadoLibre, Inc. 2.6% Bank Central Asia Tbk. PT 2.5% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.0% Samsung Electronics Co. Ltd. 7.8% Tencent Holdings Ltd. 5.3% MediaTek, Inc. 3.5% Kotak Mahindra Bank Ltd. 3.0% Reliance Industries Ltd. 3.0% WEG SA 2.8% SK Hynix, Inc. 2.7% MercadoLibre, Inc. 2.6% Bank Central Asia Tbk. PT 2.5% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Leaders Fund Class R6 | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsLeaders Fund |
| Class Name | Class R6 |
| Trading Symbol | WELIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Leaders Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Leaders Fund Class R6 $47 0.94% |
| Expenses Paid, Amount | $ 47 |
| Expense Ratio, Percent | 0.94% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 4.46% (net of fees) for the 6 months ended June 30, 2024. The Fund underperformed its benchmark, the MSCI Emerging Markets Index (net), which returned 7.49%. The Fund's benchmark is also a broad measure of market performance. nd TOP PERFORMANCE CONTRIBUTORS MediaTek Hynix Mahindra & Mahindra TOP PERFORMANCE DETRACTORS HDFC Bank BTG Pactual Totvs Globant |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $1,000,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Leaders Fund Class R6 4.46% 5.86% 1.31% 2.12% MSCI Emerging Markets Index (net) 7.49% 12.55% 3.10% 2.79% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 203,619,000 |
| Holdings Count | Holding | 62 |
| Advisory Fees Paid, Amount | $ 899,000 |
| Investment Company, Portfolio Turnover | 35% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $203,619 Number of portfolio holdings 62 Net advisory fees paid (in $000s) $899 Portfolio turnover rate (six months) 35% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the F und. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.0% Samsung Electronics Co. Ltd. 7.8% Tencent Holdings Ltd. 5.3% MediaTek, Inc. 3.5% Kotak Mahindra Bank Ltd. 3.0% Reliance Industries Ltd. 3.0% WEG SA 2.8% SK Hynix, Inc. 2.7% MercadoLibre, Inc. 2.6% Bank Central Asia Tbk. PT 2.5% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.0% Samsung Electronics Co. Ltd. 7.8% Tencent Holdings Ltd. 5.3% MediaTek, Inc. 3.5% Kotak Mahindra Bank Ltd. 3.0% Reliance Industries Ltd. 3.0% WEG SA 2.8% SK Hynix, Inc. 2.7% MercadoLibre, Inc. 2.6% Bank Central Asia Tbk. PT 2.5% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Growth Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsGrowth Fund |
| Class Name | Class I |
| Trading Symbol | WBEIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Growth Fund Class I $50 0.99% |
| Expenses Paid, Amount | $ 50 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 12.67% (net of fees) for the 6 months ended June 30, 2024 TOP PERFORMANCE CONTRIBUTORS HD Hyundai Electric Co Ltd ABB India Trent TOP PERFORMANCE DETRACTORS Bank Rakyat Indonesia AIA |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $500,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Growth Fund Class I 12.67% 17.95% 5.95% 4.22% MSCI Emerging Markets IMI (net) 7.41% 13.56% 3.93% 3.09% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 816,758,000 |
| Holdings Count | Holding | 128 |
| Advisory Fees Paid, Amount | $ 690,000 |
| Investment Company, Portfolio Turnover | 31% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $816,758 Number of portfolio holdings 128 Net advisory fees paid (in $000s) $690 Portfolio turnover rate (six months) 31% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fu nd Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.8% Tencent Holdings Ltd. 4.6% SK Hynix, Inc. 4.5% Samsung Electronics Co. Ltd. 4.4% Reliance Industries Ltd. 2.5% MercadoLibre, Inc. 2.5% Bank Central Asia Tbk. PT 2.5% MediaTek, Inc. 1.9% PDD Holdings, Inc. 1.6% NTPC Ltd. 1.5% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.8% Tencent Holdings Ltd. 4.6% SK Hynix, Inc. 4.5% Samsung Electronics Co. Ltd. 4.4% Reliance Industries Ltd. 2.5% MercadoLibre, Inc. 2.5% Bank Central Asia Tbk. PT 2.5% MediaTek, Inc. 1.9% PDD Holdings, Inc. 1.6% NTPC Ltd. 1.5% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Growth Fund Class N | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsGrowth Fund |
| Class Name | Class N |
| Trading Symbol | WBENX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Growth Fund Class N (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Growth Fund Class N $62 1.24% |
| Expenses Paid, Amount | $ 62 |
| Expense Ratio, Percent | 1.24% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 12.60% (net of fees) for the 6 months ended June 30, 2024 TOP PERFORMANCE CONTRIBUTORS HD Hyundai Electric Co Ltd ABB India Trent TOP PERFORMANCE DETRACTORS Bank Rakyat Indonesia AIA |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | GROWTH OF $10,000 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Growth Fund Class N 12.60% 17.70% 5.69% 3.96% MSCI Emerging Markets IMI (net) 7.41% 13.56% 3.93% 3.09% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 816,758,000 |
| Holdings Count | Holding | 128 |
| Advisory Fees Paid, Amount | $ 54,000 |
| Investment Company, Portfolio Turnover | 31% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $816,758 Number of portfolio holdings 128 Net advisory fees paid (in $000s) $54 Portfolio turnover rate (six months) 31% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.8% Tencent Holdings Ltd. 4.6% SK Hynix, Inc. 4.5% Samsung Electronics Co. Ltd. 4.4% Reliance Industries Ltd. 2.5% MercadoLibre, Inc. 2.5% Bank Central Asia Tbk. PT 2.5% MediaTek, Inc. 1.9% PDD Holdings, Inc. 1.6% NTPC Ltd. 1.5% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.8% Tencent Holdings Ltd. 4.6% SK Hynix, Inc. 4.5% Samsung Electronics Co. Ltd. 4.4% Reliance Industries Ltd. 2.5% MercadoLibre, Inc. 2.5% Bank Central Asia Tbk. PT 2.5% MediaTek, Inc. 1.9% PDD Holdings, Inc. 1.6% NTPC Ltd. 1.5% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Growth Fund (Class R6) | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsGrowth Fund |
| Class Name | Class R6 |
| Trading Symbol | BIEMX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Growth Fund Class R6 $47 0.94% |
| Expenses Paid, Amount | $ 47 |
| Expense Ratio, Percent | 0.94% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 12.78% (net of fees) for the 6 months ended June 30, 2024 TOP PERFORMANCE CONTRIBUTORS HD Hyundai Electric Co Ltd ABB India Trent TOP PERFORMANCE DETRACTORS Bank Rakyat Indonesia AIA |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Growth Fund Class R6 12.78% 18.06% 6.03% 4.31% MSCI Emerging Markets IMI (net) 7.41% 13.56% 3.93% 3.09% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 816,758,000 |
| Holdings Count | Holding | 128 |
| Advisory Fees Paid, Amount | $ 2,412,000 |
| Investment Company, Portfolio Turnover | 31% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $816,758 Number of portfolio holdings 128 Net advisory fees paid (in $000s) $2,412 Portfolio turnover rate (six months) 31% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.8% Tencent Holdings Ltd. 4.6% SK Hynix, Inc. 4.5% Samsung Electronics Co. Ltd. 4.4% Reliance Industries Ltd. 2.5% MercadoLibre, Inc. 2.5% Bank Central Asia Tbk. PT 2.5% MediaTek, Inc. 1.9% PDD Holdings, Inc. 1.6% NTPC Ltd. 1.5% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 11.8% Tencent Holdings Ltd. 4.6% SK Hynix, Inc. 4.5% Samsung Electronics Co. Ltd. 4.4% Reliance Industries Ltd. 2.5% MercadoLibre, Inc. 2.5% Bank Central Asia Tbk. PT 2.5% MediaTek, Inc. 1.9% PDD Holdings, Inc. 1.6% NTPC Ltd. 1.5% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets ex China Growth Fund (Class I) | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging Marketsex China Growth Fund |
| Class Name | Class I |
| Trading Symbol | WXCIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets ex China Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets ex China Growth Fund Class I $50 0.99% |
| Expenses Paid, Amount | $ 50 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 13.83% (net of fees) for the 6 months ended June 30, 2024 Outperformance was driven by a combination of country allocation and stock selection effects. Stock selection was strong within the Industrials sector, particularly electrical equipment companies HD Hyundai Electric Co and ABB India, and within the Consumer Discretionary sector. Additionally, Information Technology overweighting and Materials underweighting were notable contributors to the positive allocation effect. Partially offsetting these positive effects was negative stock selection within Financials coupled with Indonesia and Mexico overweighting. Banco BTG Pactual and Bank Rakyat Indonesia hampered relative results within the Financials sector. TOP PERFORMANCE CONTRIBUTORS HD Hyundai Electric Co Ltd ABB India delivered Trent TOP PERFORMANCE DETRACTORS Banco BTG Pactual Bank Rakyat Indonesia |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Emerging Markets ex China Growth Fund Class I 13.83% 25.12% 16.24% MSCI Emerging Markets ex-China IMI (net) 8.38% 19.32% 14.56% |
| Performance Inception Date | Jul. 29, 2022 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 25,310,000 |
| Holdings Count | Holding | 107 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 39% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $25,310 Number of portfolio holdings 107 Net advisory fees paid (in $000s) $0 Portfolio turnover rate (six months) 39% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 15.3% Samsung Electronics Co. Ltd. 4.3% SK Hynix, Inc. 3.8% MercadoLibre, Inc. 2.5% MediaTek, Inc. 2.0% Bank Central Asia Tbk. PT 1.8% Trent Ltd. 1.7% ABB India Ltd. 1.7% HD Hyundai Electric Co. Ltd. 1.5% Dixon Technologies India Ltd. 1.4% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 15.3% Samsung Electronics Co. Ltd. 4.3% SK Hynix, Inc. 3.8% MercadoLibre, Inc. 2.5% MediaTek, Inc. 2.0% Bank Central Asia Tbk. PT 1.8% Trent Ltd. 1.7% ABB India Ltd. 1.7% HD Hyundai Electric Co. Ltd. 1.5% Dixon Technologies India Ltd. 1.4% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets ex China Growth Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging Marketsex China Growth Fund |
| Class Name | Class R6 |
| Trading Symbol | WXCRX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets ex China Growth Fund Class R6 (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment) Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets ex China Growth Fund Class R6 $47 0.94% |
| Expenses Paid, Amount | $ 47 |
| Expense Ratio, Percent | 0.94% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 13.91% (net of fees) for the 6 months ended June 30, 2024 Outperformance was driven by a combination of country allocation and stock selection effects. Stock selection was strong within the Industrials sector, particularly electrical equipment companies HD Hyundai Electric Co and ABB India, and within the Consumer Discretionary sector. Additionally, Information Technology overweighting and Materials underweighting were notable contributors to the positive allocation effect. Partially offsetting these positive effects was negative stock selection within Financials coupled with Indonesia and Mexico overweighting. Banco BTG Pactual and Bank Rakyat Indonesia hampered relative results within the Financials sector. TOP PERFORMANCE CONTRIBUTORS HD Hyundai Electric Co Ltd stock ABB India Trent TOP PERFORMANCE DETRACTORS Banco BTG Pactual Bank Rakyat Indonesia |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year Since Inception Emerging Markets ex China Growth Fund Class R6 13.91% 25.22% 16.35% MSCI Emerging Markets ex-China IMI (net) 8.38% 19.32% 14.56% |
| Performance Inception Date | Jul. 29, 2022 |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 25,310,000 |
| Holdings Count | Holding | 107 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 39% |
| Additional Fund Statistics [Text Block] | Fund net assets (in $000s) $25,310 Number of portfolio holdings 107 Net advisory fees paid (in $000s) $0 Portfolio turnover rate (six months) 39% |
| Holdings [Text Block] | Graphical Representation of Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 15.3% Samsung Electronics Co. Ltd. 4.3% SK Hynix, Inc. 3.8% MercadoLibre, Inc. 2.5% MediaTek, Inc. 2.0% Bank Central Asia Tbk. PT 1.8% Trent Ltd. 1.7% ABB India Ltd. 1.7% HD Hyundai Electric Co. Ltd. 1.5% Dixon Technologies India Ltd. 1.4% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Taiwan Semiconductor Manufacturing Co. Ltd. 15.3% Samsung Electronics Co. Ltd. 4.3% SK Hynix, Inc. 3.8% MercadoLibre, Inc. 2.5% MediaTek, Inc. 2.0% Bank Central Asia Tbk. PT 1.8% Trent Ltd. 1.7% ABB India Ltd. 1.7% HD Hyundai Electric Co. Ltd. 1.5% Dixon Technologies India Ltd. 1.4% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| William Blair Emerging Markets Small Cap Growth Fund Class I | |
| Shareholder Report [Line Items] | |
| Fund Name | William Blair Emerging MarketsSmall Cap Growth Fund |
| Class Name | Class I |
| Trading Symbol | BESIX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about William Blair Emerging Markets Small Cap Growth Fund Class I (the "Fund”) for the period of January 1, 2024, to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.williamblairfunds.com |
| Additional Information Phone Number | 1-800-742-7272 |
| Additional Information Website | www.williamblairfunds.com |
| Expenses [Text Block] | What were the Fund costs for the last six months? (Based on a hypothetical $10,000 investment Fund Cost of $10,000 Investment Cost of $10,000 Investment as a percentage Emerging Markets Small Cap Growth Fund Class I $58 1.15% |
| Expenses Paid, Amount | $ 58 |
| Expense Ratio, Percent | 1.15% |
| Factors Affecting Performance [Text Block] | Management’s Discussion of Fund Performance SUMMARY OF RESULTS The Fund returned 10.32% (net of fees) for the 6 months ended June 30, 2024. The Fund outperformed its benchmark, the MSCI Emerging Markets Small Cap Index (net), which returned 7.04% and outperformed the MSCI Emerging Markets IMI ( net Outperformance was driven by a combination of country allocation and stock selection effects. Stock selection was strong within the Industrials sector, particularly electrical equipment companies HD Hyundai Electric Co and ABB India. Within Materials, Jindal Stainless was a notable contributor to relative performance. The underweight to Health Care and Materials bolstered allocation effect. Partially offsetting these positive effects was negative stock selection within Information Technology, coupled with the Mexico overweighting and Taiwan underweighting. Within Technology, semiconductor holdings were notable detractors to relative sector performance. TOP PERFORMANCE CONTRIBUTORS HD Hyundai Electric Co Ltd ABB India Jindal Stainless TOP PERFORMANCE DETRACTORS HPSP Global Unichip Totvs |
| Performance Past Does Not Indicate Future [Text] | Keep in mind that the Fund’s past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 6 Months 1 Year 5 Years 10 Years Emerging Markets Small Cap Growth Fund Class I 10.32% 20.31% 10.50% 5.93% MSCI Emerging Markets IMI (net) 7.41% 13.56% 3.93% 3.09% MSCI Emerging Markets Small Cap Index (net) 7.04% 20.04% 9.99% 5.15% |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. |
| Updated Performance Information Location [Text Block] | Visit www.williamblairfunds.com/funds/total-returns/ |
| Net Assets | $ 408,426,000 |
| Holdings Count | Holding | 130 |
| Advisory Fees Paid, Amount | $ 623,000 |
| Investment Company, Portfolio Turnover | 83% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets (in $000s) $408,426 Number of portfolio holdings 130 Net advisory fees paid (in $000s) $623 Portfolio turnover rate (six months) 83% |
| Holdings [Text Block] | Graphical Representation Holdings The tables below show the investment makeup of the Fund, representing percentage of the total net assets of the Fund. Top Ten Holdings Dixon Technologies India Ltd. 2.7% KEI Industries Ltd. 2.7% ABB India Ltd. 2.2% Wiwynn Corp. 2.1% ASPEED Technology, Inc. 2.0% Lotes Co. Ltd. 1.9% Asia Vital Components Co. Ltd. 1.8% Godrej Properties Ltd. 1.7% Huaming Power Equipment Co. Ltd. 1.6% Macrotech Developers Ltd. 1.6% Sector Allocation Geographic Diversification |
| Largest Holdings [Text Block] | Top Ten Holdings Dixon Technologies India Ltd. 2.7% KEI Industries Ltd. 2.7% ABB India Ltd. 2.2% Wiwynn Corp. 2.1% ASPEED Technology, Inc. 2.0% Lotes Co. Ltd. 1.9% Asia Vital Components Co. Ltd. 1.8% Godrej Properties Ltd. 1.7% Huaming Power Equipment Co. Ltd. 1.6% Macrotech Developers Ltd. 1.6% |
| Updated Prospectus Web Address | www.williamblairfunds.com/funds/total-returns/ |
| Shareholder Report, Line Graph (Details) - USD ($) | 6 Months Ended | ||||||||||||||||||||||||
| Jun. 30, 2024 | Mar. 31, 2024 | Dec. 31, 2023 | Sep. 30, 2023 | Aug. 17, 2023 | Jun. 30, 2023 | Mar. 31, 2023 | Dec. 31, 2022 | Sep. 30, 2022 | Jul. 29, 2022 | Jun. 30, 2022 | Mar. 16, 2022 | Dec. 31, 2021 | Aug. 27, 2021 | Jul. 17, 2021 | Jun. 30, 2021 | May 25, 2021 | Jun. 30, 2020 | Jun. 30, 2019 | May 02, 2019 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2014 | |
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small Cap Growth Fund Class R6 | ||||||||||||||||||||||||
| William Blair Emerging Markets Small Cap Growth Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Small Cap Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 889,200 | $ 739,100 | $ 667,950 | $ 900,550 | $ 603,950 | $ 539,800 | $ 585,500 | $ 549,700 | $ 488,850 | $ 545,050 | $ 500,000 | ||||||||||||||
| William Blair Emerging Markets ex China Growth Fund | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets ex China Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,338,600 | $ 1,233,700 | $ 1,175,200 | $ 1,031,000 | 1,069,000 | $ 990,000 | $ 942,000 | $ 927,000 | $ 1,000,000 | ||||||||||||||||
| William Blair Emerging Markets ex China Growth Fund (Class I) | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets ex China Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 668,150 | 615,700 | 586,950 | 515,000 | 534,000 | 494,500 | 470,500 | 463,500 | 500,000 | ||||||||||||||||
| William Blair Emerging Markets Growth Fund (Class R6) | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,525,200 | 1,291,900 | 1,321,900 | 1,961,800 | 1,301,800 | 1,138,200 | 1,157,900 | 1,040,200 | 865,100 | 989,000 | 1,000,000 | ||||||||||||||
| William Blair Emerging Markets Growth Fund Class N | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Growth Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 14,752 | 12,533 | 12,858 | 19,151 | 12,754 | 11,188 | 11,420 | 10,292 | 8,591 | 9,853 | 10,000 | ||||||||||||||
| William Blair Emerging Markets Growth Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 756,200 | 641,100 | 656,200 | 974,700 | 647,700 | 566,350 | 576,550 | 518,650 | 431,750 | 493,750 | 500,000 | ||||||||||||||
| William Blair Emerging Markets Leaders Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Leaders Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,233,200 | 1,165,000 | 1,150,900 | 1,681,600 | 1,214,800 | 1,155,500 | 1,116,200 | 1,014,600 | 866,200 | 975,900 | 1,000,000 | ||||||||||||||
| William Blair Emerging Markets Leaders Fund Class N | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Leaders Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 11,940 | 11,306 | 11,182 | 16,414 | 11,884 | 11,345 | 10,993 | 10,021 | 8,585 | 9,720 | 10,000 | ||||||||||||||
| William Blair Emerging Markets Leaders Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Leaders Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 613,300 | 579,200 | 572,200 | 837,300 | 605,250 | 576,000 | 556,400 | 506,050 | 432,250 | 487,700 | 500,000 | ||||||||||||||
| William Blair International Small Cap Growth Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Small Cap Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,355,700 | 1,313,200 | 1,135,000 | 1,791,400 | 1,252,900 | 1,142,100 | 1,215,800 | 1,115,800 | 956,700 | 970,300 | 1,000,000 | ||||||||||||||
| William Blair International Small Cap Growth Fund Class N | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Small Cap Growth Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 13,077 | 12,699 | 11,002 | 17,437 | 12,239 | 11,207 | 11,966 | 11,029 | 9,495 | 9,665 | 10,000 | ||||||||||||||
| William Blair International Small Cap Growth Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Small Cap Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 671,850 | 651,000 | 562,600 | 889,300 | 622,800 | 568,600 | 605,600 | 556,000 | 477,350 | 484,250 | 500,000 | ||||||||||||||
| William Blair Institutional International Growth Fund Institutional Class | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Institutional International Growth Fund | ||||||||||||||||||||||||
| Account Value | $ 8,053,500 | 7,441,000 | 6,465,500 | 9,244,500 | 6,477,000 | 5,874,000 | 5,868,000 | 5,271,500 | 4,548,000 | 5,003,000 | 5,000,000 | ||||||||||||||
| William Blair International Growth Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,394,800 | 1,285,300 | 1,118,100 | 1,601,500 | 1,122,300 | 1,021,000 | $ 1,000,000 | ||||||||||||||||||
| William Blair International Growth Fund Class N | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Growth Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 15,447 | 14,272 | 17,902 | 12,592 | 11,500 | 11,549 | 10,413 | 9,969 | 10,000 | ||||||||||||||||
| William Blair International Growth Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 794,750 | 732,650 | 637,700 | 913,950 | 641,000 | 583,700 | 584,250 | 525,000 | 453,500 | 499,800 | 500,000 | ||||||||||||||
| C000116470 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Leaders Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,843,600 | 1,716,100 | 1,481,300 | 2,074,400 | 1,520,200 | 1,408,000 | 1,347,000 | 1,180,700 | 997,200 | 1,024,800 | 1,000,000 | ||||||||||||||
| C000116468 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Leaders Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 17,852 | 16,666 | 14,441 | 20,273 | 14,902 | 13,845 | 13,289 | 11,688 | 9,916 | 10,214 | 10,000 | ||||||||||||||
| William Blair International Leaders Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | International Leaders Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 915,000 | 852,100 | 736,300 | 1,031,100 | 756,150 | 700,600 | 670,850 | 588,500 | 497,750 | 511,900 | 500,000 | ||||||||||||||
| C000053609 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Global Leaders Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 2,378,800 | 2,122,700 | 1,749,300 | 2,401,200 | 1,679,700 | 1,502,300 | 1,438,400 | 1,178,200 | 1,007,000 | 1,043,200 | 1,000,000 | ||||||||||||||
| C000053607 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Global Leaders Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 23,045 | 20,621 | 17,033 | 23,462 | 16,458 | 14,768 | 14,181 | 11,664 | 10,004 | 10,402 | 10,000 | ||||||||||||||
| C000053608 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Global Leaders Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 1,183,550 | 1,055,950 | 870,550 | 1,196,100 | 836,900 | 749,350 | 717,500 | 588,500 | 503,200 | 521,250 | 500,000 | ||||||||||||||
| C000211717 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small Cap Value Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,053,400 | 1,073,600 | 987,700 | 967,500 | 922,600 | $ 1,087,800 | $ 1,000,000 | ||||||||||||||||||
| C000023531 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small Cap Value Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 10,427 | 10,645 | 9,810 | 9,626 | 9,190 | 10,859 | $ 10,000 | ||||||||||||||||||
| C000023532 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small Cap Value Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 993,550 | 932,500 | 871,600 | 994,500 | 599,650 | 718,750 | 763,350 | 644,750 | 514,700 | 509,600 | 500,000 | ||||||||||||||
| C000211720 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Account Value | $ 1,596,000 | 1,414,700 | 1,165,600 | 1,611,700 | 999,500 | 998,700 | 1,000,000 | ||||||||||||||||||
| C000023540 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small Cap Growth Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 26,742 | 23,779 | 19,653 | 27,265 | 16,964 | 17,000 | 16,850 | 13,305 | 10,073 | 10,477 | 10,000 | ||||||||||||||
| C000023541 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small Cap Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 1,370,950 | 1,216,150 | 1,002,500 | 1,387,400 | 861,150 | 860,800 | 851,050 | 670,050 | 506,150 | 525,050 | 500,000 | ||||||||||||||
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Value Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,057,000 | 1,124,300 | 1,065,000 | 969,000 | $ 1,000,000 | ||||||||||||||||||||
| William Blair Small-Mid CapValue Fund CLASS I [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Value Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 528,250 | 562,400 | 532,250 | 484,500 | 500,000 | ||||||||||||||||||||
| William Blair Small-Mid Cap Growth Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,434,900 | 1,342,200 | 1,112,700 | 1,549,900 | 1,090,500 | 1,029,100 | 1,000,000 | ||||||||||||||||||
| C000023542 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Growth Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 25,289 | 23,716 | 19,725 | 27,570 | 19,455 | 18,417 | 16,796 | 13,676 | 11,189 | 11,554 | 10,000 | ||||||||||||||
| C000023543 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 1,297,650 | 1,213,950 | 1,006,950 | 1,403,600 | 988,000 | 933,050 | 848,950 | 689,650 | 562,500 | 579,300 | 500,000 | ||||||||||||||
| Small-Mid Cap Core Fund Class R6 [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Core Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,536,100 | 1,534,100 | 1,464,100 | 1,354,000 | 1,277,900 | 1,633,200 | 1,526,100 | ||||||||||||||||||
| William Blair Small-Mid Cap Core Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Core Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 1,370,950 | 1,216,150 | 1,002,500 | 1,387,400 | 861,150 | 860,800 | |||||||||||||||||||
| William Blair Mid Cap Value Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Mid Cap Value Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,069,600 | 1,138,400 | 1,052,200 | 949,200 | 983,500 | 937,000 | 929,900 | 821,000 | 874,000 | $ 1,000,000 | |||||||||||||||
| William Blair Mid Cap Value Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Mid Cap Value Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 534,400 | 568,800 | 525,700 | 473,950 | 491,650 | 468,400 | 464,350 | 410,500 | 437,000 | 500,000 | |||||||||||||||
| William Blair Large Cap Growth Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Large Cap Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 2,293,700 | 1,695,000 | 1,368,000 | 1,783,900 | 1,253,600 | 1,040,300 | 1,000,000 | ||||||||||||||||||
| William Blair Large Cap Growth Fund Class N | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Large Cap Growth Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 43,185 | 32,017 | 25,926 | 33,906 | 23,884 | 19,881 | 17,137 | 13,105 | 11,391 | 11,296 | 10,000 | ||||||||||||||
| William Blair Large Cap Growth Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Large Cap Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 2,214,900 | 1,638,250 | 1,322,400 | 1,725,050 | 1,212,500 | 1,006,650 | 865,350 | 660,500 | 572,100 | 566,500 | 500,000 | ||||||||||||||
| William Blair Growth Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 2,057,000 | 1,648,400 | 1,327,100 | 1,712,900 | 1,196,000 | 1,025,300 | 1,000,000 | ||||||||||||||||||
| William Blair China Growth Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | China Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 504,200 | 488,100 | 547,400 | 645,400 | 777,000 | 956,000 | $ 1,000,000 | ||||||||||||||||||
| William Blair China Growth Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | China Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 252,600 | 244,550 | 274,500 | 323,000 | 388,500 | 478,000 | 500,000 | ||||||||||||||||||
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Small Cap Growth Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 1,790,100 | 1,486,600 | 1,343,100 | 1,809,600 | 1,212,900 | 1,083,600 | 1,174,700 | 1,101,700 | 979,500 | 1,090,600 | 1,000,000 | ||||||||||||||
| William Blair Emerging Markets Small Cap Growth Fund Class N | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Small Cap Growth Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 17,310 | 14,413 | 13,065 | 17,656 | 11,875 | 10,637 | 11,569 | 10,891 | 9,722 | 10,870 | 10,000 | ||||||||||||||
| William Blair Emerging Markets Debt Fund Class R6 | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Debt Fund Class R6 | ||||||||||||||||||||||||
| Account Value | $ 967,400 | 929,700 | 861,400 | 819,200 | 782,900 | 986,600 | 1,003,700 | $ 1,000,000 | |||||||||||||||||
| William Blair Emerging Markets Debt Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Debt Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 483,150 | 464,400 | 430,450 | 409,400 | 391,100 | 493,000 | 501,850 | 500,000 | |||||||||||||||||
| William Blair Growth Fund Class N | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Growth Fund Class N | ||||||||||||||||||||||||
| Account Value | $ 33,873 | 27,224 | 21,985 | 28,497 | 19,963 | 17,184 | 15,064 | 11,950 | 10,643 | 10,615 | 10,000 | ||||||||||||||
| William Blair Growth Fund Class I | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Growth Fund Class I | ||||||||||||||||||||||||
| Account Value | $ 1,743,900 | 1,398,150 | 1,125,700 | 1,454,050 | 1,015,950 | 872,300 | 762,300 | 603,100 | 535,550 | 532,350 | 500,000 | ||||||||||||||
| MSCI Emerging Markets Small Cap Index (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | MSCI Emerging Markets Small Cap Index (net) | ||||||||||||||||||||||||
| Account Value | $ 826,350 | 688,400 | 607,700 | 766,500 | 468,100 | 513,400 | 541,050 | 512,200 | 437,650 | 501,700 | 500,000 | ||||||||||||||
| MSCI Emerging Markets ex-China IMI (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | MSCI Emerging Markets ex-China IMI (net) | ||||||||||||||||||||||||
| Account Value | $ 649,450 | 620,850 | 599,250 | 532,750 | 544,300 | 511,300 | 492,650 | 457,000 | $ 500,000 | ||||||||||||||||
| MSCI Emerging Markets IMI (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | MSCI Emerging Markets IMI (net) | ||||||||||||||||||||||||
| Account Value | $ 677,800 | 596,850 | 578,400 | 768,700 | 536,750 | 558,950 | 556,300 | 515,600 | 419,800 | 477,950 | 500,000 | ||||||||||||||
| MSCI Emerging Markets Index (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | MSCI Emerging Markets Index (net) | ||||||||||||||||||||||||
| Account Value | $ 658,500 | 585,050 | 575,000 | 769,600 | 546,200 | 565,350 | 558,600 | 516,250 | 417,200 | 474,400 | 500,000 | ||||||||||||||
| MSCI All Country World Ex-U.S. Small Cap Index (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | MSCI All Country World ex-U.S. Small Cap Index (net) | ||||||||||||||||||||||||
| Account Value | $ 771,800 | 693,700 | 625,350 | 806,350 | 548,400 | 573,300 | 609,550 | 551,250 | 458,200 | 484,650 | 500,000 | ||||||||||||||
| International Growth Fund Class N [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Account Value | 12,453 | ||||||||||||||||||||||||
| MSCI All Country World Ex-U.S. IMI (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Account Value | $ 734,350 | 658,200 | 585,200 | 730,200 | 532,300 | 558,750 | 557,300 | 517,250 | 429,500 | 475,150 | 500,000 | ||||||||||||||
| MSCI All Country World IMI (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | MSCI All Country World IMI (net) | ||||||||||||||||||||||||
| Account Value | $ 1,096,900 | 926,450 | 797,700 | 955,600 | 678,050 | 670,150 | 640,950 | 576,650 | 484,550 | 504,050 | 500,000 | ||||||||||||||
| Russell 2000 Value Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Russell 2000® Value Index | ||||||||||||||||||||||||
| Account Value | $ 914,700 | 824,850 | 778,100 | 929,400 | 536,350 | 649,950 | 693,150 | 612,900 | 490,850 | 503,900 | 500,000 | ||||||||||||||
| Russell 3000 Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Russell 3000® Index | ||||||||||||||||||||||||
| Account Value | $ 649,700 | 629,450 | 572,150 | 510,500 | 527,700 | 486,850 | 454,250 | 423,800 | 443,600 | 500,000 | 1,247,450 | 865,300 | 812,300 | 1,000,000 | 745,350 | 649,350 | 547,950 | 536,450 | 500,000 | ||||||
| Russell 2000 Growth Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Account Value | $ 1,020,000 | 934,600 | 788,500 | 1,184,500 | 782,550 | 756,250 | $ 1,000,000 | 760,000 | 623,650 | 501,300 | 561,700 | 500,000 | |||||||||||||
| Russell 2500 Value Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Russell 2500® Value Index | ||||||||||||||||||||||||
| Account Value | $ 561,150 | 586,400 | 552,850 | 485,950 | $ 500,000 | ||||||||||||||||||||
| Russell Midcap Value Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Russell Midcap® Value Index | ||||||||||||||||||||||||
| Account Value | $ 553,300 | $ 572,800 | 529,250 | $ 472,100 | 494,100 | $ 475,750 | 469,550 | $ 425,100 | 447,150 | $ 500,000 | |||||||||||||||
| Russell 1000 Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Russell 1000® Index | ||||||||||||||||||||||||
| Account Value | $ 1,625,200 | 1,311,950 | 1,099,100 | 1,263,850 | 883,350 | 821,900 | 747,050 | 652,200 | 552,600 | 536,850 | 500,000 | ||||||||||||||
| Russell 1000 Growth Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Russell 1000® Growth Index | ||||||||||||||||||||||||
| Account Value | $ 2,269,200 | 1,700,000 | 1,337,450 | 1,646,600 | 1,155,500 | 937,300 | 840,200 | 685,800 | 569,500 | 552,800 | 500,000 | ||||||||||||||
| MSCI China All Shares Index (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | MSCI China All Shares Index (net) | ||||||||||||||||||||||||
| Account Value | $ 334,550 | 327,100 | 349,900 | 369,700 | 426,950 | 483,950 | $ 500,000 | ||||||||||||||||||
| Bloomberg Global Aggregate Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Bloomberg Global Aggregate Index | ||||||||||||||||||||||||
| Account Value | $ 418,400 | 432,050 | 414,550 | 408,700 | 420,100 | 487,950 | 495,650 | 500,000 | |||||||||||||||||
| JPMorgan Emerging Markets Bond Index (EMBI) Global Diversified (net) [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | JPMorgan Emerging Markets Bond Index (EMBI) Global Diversified (net) | ||||||||||||||||||||||||
| Account Value | $ 466,300 | $ 455,600 | 426,900 | $ 410,150 | 397,550 | $ 498,850 | 504,600 | $ 500,000 | |||||||||||||||||
| Standard & Poor's 500 Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | S&P 500® Index | ||||||||||||||||||||||||
| Account Value | $ 1,676,050 | 1,345,600 | 1,125,150 | 1,258,750 | 894,050 | 831,650 | 753,200 | 658,500 | 558,550 | 537,100 | 500,000 | ||||||||||||||
| Russell 3000 Growth Index [Member] | |||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||
| Line Graph and Table Measure Name | Russell 3000® Growth Index | ||||||||||||||||||||||||
| Account Value | $ 2,158,900 | $ 1,632,850 | $ 1,289,750 | $ 1,607,700 | $ 1,124,350 | $ 922,050 | $ 833,650 | $ 680,700 | $ 563,850 | $ 553,450 | $ 500,000 |
| Shareholder Report, Average Annual Return (Details) | 6 Months Ended | 10 Months Ended | 12 Months Ended | 23 Months Ended | 28 Months Ended | 34 Months Ended | 35 Months Ended | 37 Months Ended | 57 Months Ended | 60 Months Ended | 62 Months Ended | 120 Months Ended |
| Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | |
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small Cap Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 7.88% | 12.82% | 9.83% | 9.47% | ||||||||
| William Blair Emerging Markets Small Cap Growth Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Small Cap Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 10.32% | 20.31% | 10.50% | 5.93% | ||||||||
| William Blair Emerging Markets ex China Growth Fund | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets ex China Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 13.91% | 25.22% | 16.35% | |||||||||
| William Blair Emerging Markets ex China Growth Fund (Class I) | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets ex China Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 13.83% | 25.12% | 16.24% | |||||||||
| William Blair Emerging Markets Growth Fund (Class R6) | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 12.78% | 18.06% | 6.03% | 4.31% | ||||||||
| William Blair Emerging Markets Growth Fund Class N | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Growth Fund Class N | |||||||||||
| Average Annual Return, Percent | 12.60% | 17.70% | 5.69% | 3.96% | ||||||||
| William Blair Emerging Markets Growth Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 12.67% | 17.95% | 5.95% | 4.22% | ||||||||
| William Blair Emerging Markets Leaders Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Leaders Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 4.46% | 5.86% | 1.31% | 2.12% | ||||||||
| William Blair Emerging Markets Leaders Fund Class N | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Leaders Fund Class N | |||||||||||
| Average Annual Return, Percent | 4.47% | 5.61% | 1.03% | 1.79% | ||||||||
| William Blair Emerging Markets Leaders Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Leaders Fund Class I | |||||||||||
| Average Annual Return, Percent | 4.45% | 5.89% | 1.26% | 2.06% | ||||||||
| William Blair International Small Cap Growth Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Small Cap Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | (2.09%) | 3.24% | 3.49% | 3.09% | ||||||||
| William Blair International Small Cap Growth Fund Class N | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Small Cap Growth Fund Class N | |||||||||||
| Average Annual Return, Percent | (2.21%) | 2.97% | 3.13% | 2.72% | ||||||||
| William Blair International Small Cap Growth Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Small Cap Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | (2.10%) | 3.20% | 3.39% | 3% | ||||||||
| William Blair Institutional International Growth Fund Institutional Class | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Institutional International Growth Fund | |||||||||||
| Average Annual Return, Percent | 4.58% | 8.24% | 6.51% | 4.88% | ||||||||
| William Blair International Growth Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 4.60% | 8.52% | 6.44% | 6.65% | ||||||||
| William Blair International Growth Fund Class N | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Growth Fund Class N | |||||||||||
| Average Annual Return, Percent | 4.47% | 8.23% | 6.08% | 4.44% | ||||||||
| William Blair International Growth Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 4.60% | 8.48% | 6.37% | 4.74% | ||||||||
| C000116470 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Leaders Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 5.96% | 7.43% | 5.54% | 6.31% | ||||||||
| C000116468 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Leaders Fund Class N | |||||||||||
| Average Annual Return, Percent | 5.81% | 7.11% | 5.22% | 5.97% | ||||||||
| William Blair International Leaders Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | International Leaders Fund Class I | |||||||||||
| Average Annual Return, Percent | 5.97% | 7.38% | 5.48% | 6.23% | ||||||||
| C000053609 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Global Leaders Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 8.06% | 12.06% | 9.63% | 9.05% | ||||||||
| C000053607 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Global Leaders Fund Class N | |||||||||||
| Average Annual Return, Percent | 7.96% | 11.75% | 9.31% | 8.71% | ||||||||
| C000053608 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Global Leaders Fund Class I | |||||||||||
| Average Annual Return, Percent | 8.06% | 12.08% | 9.57% | 9% | ||||||||
| C000211717 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small Cap Value Fund Class R6 | |||||||||||
| Average Annual Return, Percent | (1.88%) | 6.64% | 1.78% | |||||||||
| C000023531 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small Cap Value Fund Class N | |||||||||||
| Average Annual Return, Percent | (2.05%) | 6.29% | 1.43% | |||||||||
| C000023532 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small Cap Value Fund Class I | |||||||||||
| Average Annual Return, Percent | (1.95%) | 6.54% | 6.69% | 7.11% | ||||||||
| C000023540 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small Cap Growth Fund Class N | |||||||||||
| Average Annual Return, Percent | 7.71% | 12.46% | 9.48% | 10.34% | ||||||||
| C000023541 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small Cap Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 7.84% | 12.73% | 9.76% | 10.61% | ||||||||
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Value Fund Class R6 | |||||||||||
| Average Annual Return, Percent | (0.75%) | 5.70% | ||||||||||
| William Blair Small-Mid CapValue Fund CLASS I [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Value Fund Class I | |||||||||||
| Average Annual Return, Percent | (0.75%) | 5.65% | ||||||||||
| William Blair Small-Mid Cap Growth Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 1.34% | 6.90% | 6.87% | 7.24% | ||||||||
| Small-Mid Cap Growth Fund Class N [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Growth Fund Class N | |||||||||||
| Average Annual Return, Percent | 1.20% | 6.63% | 6.55% | 9.72% | ||||||||
| C000023543 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 1.34% | 6.89% | 6.82% | 10.01% | ||||||||
| Small-Mid Cap Core Fund Class R6 [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Core Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 0.13% | 4.92% | 9.46% | |||||||||
| William Blair Small-Mid Cap Core Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Small-Mid Cap Core Fund Class I | |||||||||||
| Average Annual Return, Percent | 0.07% | 4.88% | 9.41% | |||||||||
| William Blair Mid Cap Value Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Mid Cap Value Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 1.66% | 8.75% | 2.97% | |||||||||
| William Blair Mid Cap Value Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Mid Cap Value Fund Class I | |||||||||||
| Average Annual Return, Percent | 1.66% | 8.70% | 2.94% | |||||||||
| William Blair Large Cap Growth Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Large Cap Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 20.50% | 35.32% | 17.13% | 17.44% | ||||||||
| William Blair Large Cap Growth Fund Class N | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Large Cap Growth Fund Class N | |||||||||||
| Average Annual Return, Percent | 20.31% | 34.88% | 16.78% | 15.75% | ||||||||
| William Blair Large Cap Growth Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Large Cap Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 20.50% | 35.20% | 17.08% | 16.05% | ||||||||
| William Blair Growth Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 13.87% | 24.79% | 14.94% | 14.99% | ||||||||
| William Blair China Growth Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | China Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 3.30% | (7.89%) | (21.40%) | |||||||||
| William Blair China Growth Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | China Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 3.29% | (7.98%) | (21.35%) | |||||||||
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Small Cap Growth Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 10.34% | 20.42% | 10.56% | 6% | ||||||||
| William Blair Emerging Markets Small Cap Growth Fund Class N | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Small Cap Growth Fund Class N | |||||||||||
| Average Annual Return, Percent | 10.22% | 20.10% | 10.23% | 5.64% | ||||||||
| William Blair Emerging Markets Debt Fund Class R6 | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Debt Fund Class R6 | |||||||||||
| Average Annual Return, Percent | 4.05% | 12.28% | (1.05%) | |||||||||
| William Blair Emerging Markets Debt Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Emerging Markets Debt Fund Class I | |||||||||||
| Average Annual Return, Percent | 4.02% | 12.20% | (1.10%) | |||||||||
| William Blair Growth Fund Class N | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Growth Fund Class N | |||||||||||
| Average Annual Return, Percent | 13.61% | 24.42% | 14.54% | 12.98% | ||||||||
| William Blair Growth Fund Class I | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Growth Fund Class I | |||||||||||
| Average Annual Return, Percent | 13.86% | 24.73% | 14.86% | 13.31% | ||||||||
| MSCI Emerging Markets Small Cap Index (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | MSCI Emerging Markets Small Cap Index (net) | |||||||||||
| Average Annual Return, Percent | 7.04% | 20.04% | 9.99% | 5.15% | ||||||||
| MSCI Emerging Markets ex-China IMI (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | MSCI Emerging Markets ex-China IMI (net) | |||||||||||
| Average Annual Return, Percent | 8.38% | 19.32% | 14.56% | |||||||||
| MSCI Emerging Markets IMI (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | MSCI Emerging Markets IMI (net) | |||||||||||
| Average Annual Return, Percent | 7.41% | 13.56% | 3.93% | 3.09% | ||||||||
| MSCI Emerging Markets Index (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | MSCI Emerging Markets Index (net) | |||||||||||
| Average Annual Return, Percent | 7.49% | 12.55% | 3.10% | 2.79% | ||||||||
| MSCI All Country World ex-U.S. Small Cap Index (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Average Annual Return, Percent | 2.78% | 11.26% | 6.13% | 4.44% | ||||||||
| MSCI All Country World ex-U.S. IMI (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | MSCI All Country World ex-U.S. IMI (net) | |||||||||||
| Average Annual Return, Percent | 5.28% | 11.57% | 5.62% | 3.92% | ||||||||
| MSCI All Country World IMI (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | MSCI All Country World IMI (net) | |||||||||||
| Average Annual Return, Percent | 10.28% | 18.40% | 10.36% | 8.17% | ||||||||
| Russell 2000 Value Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell 2000® Value Index | |||||||||||
| Average Annual Return, Percent | (0.85%) | 10.90% | 7.07% | 6.23% | ||||||||
| Russell 3000 Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell 3000® Index | |||||||||||
| Average Annual Return, Percent | 13.56% | 23.13% | 12.09% | 13.84% | ||||||||
| Russell 2000 Growth Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Average Annual Return, Percent | 6.12% | |||||||||||
| Russell 2500 Value Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell 2500® Value Index | |||||||||||
| Average Annual Return, Percent | 1.50% | 12.22% | ||||||||||
| Russell 2500 Growth Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell 2500™ Growth Index | |||||||||||
| Average Annual Return, Percent | 3.93% | 9.02% | 7.58% | 8.77% | ||||||||
| Russell 2500 Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell 2500™ Index | |||||||||||
| Average Annual Return, Percent | 2.35% | 10.47% | 9.06% | |||||||||
| Russell Midcap Value Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell Midcap® Value Index | |||||||||||
| Average Annual Return, Percent | 4.54% | 11.98% | 4.52% | |||||||||
| Russell 1000 Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell 1000® Index | |||||||||||
| Average Annual Return, Percent | 14.24% | 23.88% | 14.61% | 14.31% | 12.51% | |||||||
| Russell 1000 Growth Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell 1000® Growth Index | |||||||||||
| Average Annual Return, Percent | 20.70% | 33.48% | 19.34% | 18.86% | 16.33% | |||||||
| Standard & Poor's 500 Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | S&P 500® Index | |||||||||||
| Average Annual Return, Percent | 15.29% | 24.56% | 15.05% | 14.76% | 12.86% | |||||||
| Russell 3000 Growth Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Russell 3000® Growth Index | |||||||||||
| Average Annual Return, Percent | 19.90% | 32.22% | 18.55% | 18.09% | 15.75% | |||||||
| MSCI China All Shares Index (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | MSCI China All Shares Index (net) | |||||||||||
| Average Annual Return, Percent | 2.28% | (4.39%) | (13.18%) | |||||||||
| Bloomberg Global Aggregate Index [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | Bloomberg Global Aggregate Index | |||||||||||
| Average Annual Return, Percent | (3.16%) | 0.93% | (5.58%) | |||||||||
| JPMorgan Emerging Markets Bond Index (EMBI) Global Diversified (net) [Member] | ||||||||||||
| Average Annual Return [Line Items] | ||||||||||||
| Line Graph and Table Measure Name | JPMorgan Emerging Markets Bond Index (EMBI) Global Diversified (net) | |||||||||||
| Average Annual Return, Percent | 2.34% | 9.23% | (2.22%) |
| Shareholder Report, Holdings (Details) | Jun. 30, 2024 |
| Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.60% |
| Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.60% |
| Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.80% |
| Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.70% |
| Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.30% |
| Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.20% |
| William Blair Growth Fund Class I | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.80% |
| William Blair Growth Fund Class I | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8% |
| William Blair Growth Fund Class I | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| William Blair Growth Fund Class I | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| William Blair Growth Fund Class I | Advanced Micro Devices, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Growth Fund Class I | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| William Blair Growth Fund Class I | Apple, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Growth Fund Class I | UnitedHealth Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.30% |
| William Blair Growth Fund Class I | Palo Alto Networks, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Growth Fund Class I | ServiceNow, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Growth Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 41.80% |
| William Blair Growth Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| William Blair Growth Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.10% |
| William Blair Growth Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.50% |
| William Blair Growth Fund Class I | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.40% |
| William Blair Growth Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.30% |
| William Blair Growth Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| William Blair Growth Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Growth Fund Class N | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.80% |
| William Blair Growth Fund Class N | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8% |
| William Blair Growth Fund Class N | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| William Blair Growth Fund Class N | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| William Blair Growth Fund Class N | Advanced Micro Devices, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Growth Fund Class N | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| William Blair Growth Fund Class N | Apple, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Growth Fund Class N | UnitedHealth Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.30% |
| William Blair Growth Fund Class N | Palo Alto Networks, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Growth Fund Class N | ServiceNow, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Growth Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 41.80% |
| William Blair Growth Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| William Blair Growth Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.10% |
| William Blair Growth Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.50% |
| William Blair Growth Fund Class N | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.40% |
| William Blair Growth Fund Class N | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.30% |
| William Blair Growth Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| William Blair Growth Fund Class N | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Emerging Markets Debt Fund Class I | Petroleos Mexicanos [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Emerging Markets Debt Fund Class I | Qatar Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Debt Fund Class I | Romania Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair Emerging Markets Debt Fund Class I | Panama Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair Emerging Markets Debt Fund Class I | Argentine Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair Emerging Markets Debt Fund Class I | Paraguay Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Debt Fund Class I | South Africa Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Debt Fund Class I | Oman Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Debt Fund Class I | Turkiye Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Emerging Markets Debt Fund Class I | Dominican Republic International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, AAA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.90% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.80% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, BB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 24.30% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, B Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21.50% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, CCC Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.20% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, CC Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Emerging Markets Debt Fund Class I | Standard & Poor's, D Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Emerging Markets Debt Fund Class I | Not Rated [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Emerging Markets Debt Fund Class I | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 41.30% |
| William Blair Emerging Markets Debt Fund Class I | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 37.10% |
| William Blair Emerging Markets Debt Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.20% |
| William Blair Emerging Markets Debt Fund Class R6 | Petroleos Mexicanos [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Emerging Markets Debt Fund Class R6 | Qatar Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Debt Fund Class R6 | Romania Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair Emerging Markets Debt Fund Class R6 | Panama Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair Emerging Markets Debt Fund Class R6 | Argentine Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair Emerging Markets Debt Fund Class R6 | Paraguay Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Debt Fund Class R6 | South Africa Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Debt Fund Class R6 | Oman Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Debt Fund Class R6 | Turkiye Government International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Emerging Markets Debt Fund Class R6 | Dominican Republic International Bond [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, AAA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.90% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.80% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, BB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 24.30% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, B Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21.50% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, CCC Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.20% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, CC Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Emerging Markets Debt Fund Class R6 | Standard & Poor's, D Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Emerging Markets Debt Fund Class R6 | Not Rated [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Emerging Markets Debt Fund Class R6 | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 41.30% |
| William Blair Emerging Markets Debt Fund Class R6 | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 37.10% |
| William Blair Emerging Markets Debt Fund Class R6 | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | ASPEED Technology, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Dixon Technologies India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | KEI Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | ABB India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Wiwynn Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Lotes Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Asia Vital Components Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Godrej Properties Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Huaming Power Equipment Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Macrotech Developers Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 15.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 31.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Financial Services [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.80% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.30% |
| William Blair Emerging Markets Small Cap Growth Fund Class N | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 81.50% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | ASPEED Technology, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Dixon Technologies India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | KEI Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | ABB India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Wiwynn Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Lotes Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Asia Vital Components Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Godrej Properties Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Huaming Power Equipment Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Macrotech Developers Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 15.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 31.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Financial Services [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.80% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.30% |
| William Blair Emerging Markets Small Cap Growth Fund Class R6 | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 81.50% |
| William Blair China Growth Fund Class I | Tencent Holdings Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| William Blair China Growth Fund Class I | NetEase, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| William Blair China Growth Fund Class I | Kweichow Moutai Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| William Blair China Growth Fund Class I | PDD Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| William Blair China Growth Fund Class I | Huaneng Lancang River Hydropower, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| William Blair China Growth Fund Class I | NAURA Technology Group Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair China Growth Fund Class I | Weichai Power Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair China Growth Fund Class I | Contemporary Amperex Technology Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| William Blair China Growth Fund Class I | Zhongji Innolight Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair China Growth Fund Class I | Yutong Bus Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair China Growth Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| William Blair China Growth Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| William Blair China Growth Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.80% |
| William Blair China Growth Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.50% |
| William Blair China Growth Fund Class I | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.90% |
| William Blair China Growth Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.30% |
| William Blair China Growth Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.30% |
| William Blair China Growth Fund Class I | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| William Blair China Growth Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97.70% |
| William Blair China Growth Fund Class R6 | Tencent Holdings Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| William Blair China Growth Fund Class R6 | NetEase, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| William Blair China Growth Fund Class R6 | Kweichow Moutai Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| William Blair China Growth Fund Class R6 | PDD Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| William Blair China Growth Fund Class R6 | Huaneng Lancang River Hydropower, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| William Blair China Growth Fund Class R6 | NAURA Technology Group Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair China Growth Fund Class R6 | Weichai Power Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair China Growth Fund Class R6 | Contemporary Amperex Technology Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| William Blair China Growth Fund Class R6 | Zhongji Innolight Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair China Growth Fund Class R6 | Yutong Bus Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair China Growth Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| William Blair China Growth Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| William Blair China Growth Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.80% |
| William Blair China Growth Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.50% |
| William Blair China Growth Fund Class R6 | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.90% |
| William Blair China Growth Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.30% |
| William Blair China Growth Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.30% |
| William Blair China Growth Fund Class R6 | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| William Blair China Growth Fund Class R6 | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97.70% |
| William Blair Growth Fund Class R6 | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.80% |
| William Blair Growth Fund Class R6 | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8% |
| William Blair Growth Fund Class R6 | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| William Blair Growth Fund Class R6 | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| William Blair Growth Fund Class R6 | Advanced Micro Devices, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Growth Fund Class R6 | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| William Blair Growth Fund Class R6 | Apple, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Growth Fund Class R6 | UnitedHealth Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.30% |
| William Blair Growth Fund Class R6 | Palo Alto Networks, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Growth Fund Class R6 | ServiceNow, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Growth Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 41.80% |
| William Blair Growth Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| William Blair Growth Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.10% |
| William Blair Growth Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.50% |
| William Blair Growth Fund Class R6 | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.40% |
| William Blair Growth Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.30% |
| William Blair Growth Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| William Blair Growth Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Large Cap Growth Fund Class I | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.90% |
| William Blair Large Cap Growth Fund Class I | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.70% |
| William Blair Large Cap Growth Fund Class I | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| William Blair Large Cap Growth Fund Class I | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.70% |
| William Blair Large Cap Growth Fund Class I | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Large Cap Growth Fund Class I | Apple, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| William Blair Large Cap Growth Fund Class I | UnitedHealth Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Large Cap Growth Fund Class I | ServiceNow, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Large Cap Growth Fund Class I | Intuit, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Large Cap Growth Fund Class I | Lam Research Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Large Cap Growth Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 48.50% |
| William Blair Large Cap Growth Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.50% |
| William Blair Large Cap Growth Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.60% |
| William Blair Large Cap Growth Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.30% |
| William Blair Large Cap Growth Fund Class I | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.30% |
| William Blair Large Cap Growth Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| William Blair Large Cap Growth Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Large Cap Growth Fund Class I | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| William Blair Large Cap Growth Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.30% |
| William Blair Large Cap Growth Fund Class N | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.90% |
| William Blair Large Cap Growth Fund Class N | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.70% |
| William Blair Large Cap Growth Fund Class N | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| William Blair Large Cap Growth Fund Class N | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.70% |
| William Blair Large Cap Growth Fund Class N | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Large Cap Growth Fund Class N | Apple, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| William Blair Large Cap Growth Fund Class N | UnitedHealth Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Large Cap Growth Fund Class N | ServiceNow, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Large Cap Growth Fund Class N | Intuit, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Large Cap Growth Fund Class N | Lam Research Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Large Cap Growth Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 48.50% |
| William Blair Large Cap Growth Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.50% |
| William Blair Large Cap Growth Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.60% |
| William Blair Large Cap Growth Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.30% |
| William Blair Large Cap Growth Fund Class N | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.30% |
| William Blair Large Cap Growth Fund Class N | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| William Blair Large Cap Growth Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Large Cap Growth Fund Class N | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| William Blair Large Cap Growth Fund Class N | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.30% |
| William Blair Large Cap Growth Fund Class R6 | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.90% |
| William Blair Large Cap Growth Fund Class R6 | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.70% |
| William Blair Large Cap Growth Fund Class R6 | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.70% |
| William Blair Large Cap Growth Fund Class R6 | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.70% |
| William Blair Large Cap Growth Fund Class R6 | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Large Cap Growth Fund Class R6 | Apple, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| William Blair Large Cap Growth Fund Class R6 | UnitedHealth Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Large Cap Growth Fund Class R6 | ServiceNow, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Large Cap Growth Fund Class R6 | Intuit, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Large Cap Growth Fund Class R6 | Lam Research Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Large Cap Growth Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 48.50% |
| William Blair Large Cap Growth Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.50% |
| William Blair Large Cap Growth Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.60% |
| William Blair Large Cap Growth Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.30% |
| William Blair Large Cap Growth Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| William Blair Large Cap Growth Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| William Blair Large Cap Growth Fund Class R6 | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| William Blair Large Cap Growth Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.30% |
| William Blair Large Cap Growth Fund Class R6 | Financial Service Others [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| William Blair Mid Cap Value Fund Class I | Qorvo, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Mid Cap Value Fund Class I | Willis Towers Watson PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Mid Cap Value Fund Class I | Ingredion, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Mid Cap Value Fund Class I | Timken Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Mid Cap Value Fund Class I | KKR & Co., Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Mid Cap Value Fund Class I | U.S. Foods Holding Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class I | Axalta Coating Systems Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class I | NiSource, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class I | Diamondback Energy, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class I | Teleflex, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.40% |
| William Blair Mid Cap Value Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.10% |
| William Blair Mid Cap Value Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.80% |
| William Blair Mid Cap Value Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.50% |
| William Blair Mid Cap Value Fund Class I | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.50% |
| William Blair Mid Cap Value Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| William Blair Mid Cap Value Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.30% |
| William Blair Mid Cap Value Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.80% |
| William Blair Mid Cap Value Fund Class I | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| William Blair Mid Cap Value Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.90% |
| William Blair Mid Cap Value Fund Class I | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.50% |
| William Blair Mid Cap Value Fund Class R6 | Qorvo, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Mid Cap Value Fund Class R6 | Willis Towers Watson PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Mid Cap Value Fund Class R6 | Ingredion, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Mid Cap Value Fund Class R6 | Timken Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Mid Cap Value Fund Class R6 | KKR & Co., Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Mid Cap Value Fund Class R6 | U.S. Foods Holding Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class R6 | Axalta Coating Systems Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class R6 | NiSource, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class R6 | Diamondback Energy, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class R6 | Teleflex, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Mid Cap Value Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.40% |
| William Blair Mid Cap Value Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.10% |
| William Blair Mid Cap Value Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.80% |
| William Blair Mid Cap Value Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.50% |
| William Blair Mid Cap Value Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| William Blair Mid Cap Value Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.30% |
| William Blair Mid Cap Value Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.80% |
| William Blair Mid Cap Value Fund Class R6 | Financial Services [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.50% |
| William Blair Mid Cap Value Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.90% |
| William Blair Mid Cap Value Fund Class R6 | Real Estate Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| William Blair Mid Cap Value Fund Class R6 | Public utility [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.50% |
| William Blair Small-Mid Cap Core Fund Class I | BWX Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Small-Mid Cap Core Fund Class I | Baldwin Insurance Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair Small-Mid Cap Core Fund Class I | Everest Group Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Small-Mid Cap Core Fund Class I | Western Alliance Bancorp [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Small-Mid Cap Core Fund Class I | Bright Horizons Family Solutions, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Small-Mid Cap Core Fund Class I | Carlyle Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Small-Mid Cap Core Fund Class I | Casella Waste Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Small-Mid Cap Core Fund Class I | Garrett Motion, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small-Mid Cap Core Fund Class I | East West Bancorp, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small-Mid Cap Core Fund Class I | ACV Auctions, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small-Mid Cap Core Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.10% |
| William Blair Small-Mid Cap Core Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.50% |
| William Blair Small-Mid Cap Core Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| William Blair Small-Mid Cap Core Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22.10% |
| William Blair Small-Mid Cap Core Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| William Blair Small-Mid Cap Core Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| William Blair Small-Mid Cap Core Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| William Blair Small-Mid Cap Core Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| William Blair Small-Mid Cap Core Fund Class I | Financial Service Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.40% |
| William Blair Small-Mid Cap Core Fund Class I | Real Estate Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| William Blair Small-Mid Cap Core Fund Class I | Public utility [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Small-Mid Cap Core Fund Class R6 [Member] | BWX Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| Small-Mid Cap Core Fund Class R6 [Member] | Baldwin Insurance Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Small-Mid Cap Core Fund Class R6 [Member] | Everest Group Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| Small-Mid Cap Core Fund Class R6 [Member] | Western Alliance Bancorp [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Small-Mid Cap Core Fund Class R6 [Member] | Bright Horizons Family Solutions, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| Small-Mid Cap Core Fund Class R6 [Member] | Carlyle Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| Small-Mid Cap Core Fund Class R6 [Member] | Casella Waste Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| Small-Mid Cap Core Fund Class R6 [Member] | Garrett Motion, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Small-Mid Cap Core Fund Class R6 [Member] | East West Bancorp, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| Small-Mid Cap Core Fund Class R6 [Member] | ACV Auctions, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Small-Mid Cap Core Fund Class R6 [Member] | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.10% |
| Small-Mid Cap Core Fund Class R6 [Member] | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.50% |
| Small-Mid Cap Core Fund Class R6 [Member] | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| Small-Mid Cap Core Fund Class R6 [Member] | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22.10% |
| Small-Mid Cap Core Fund Class R6 [Member] | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Small-Mid Cap Core Fund Class R6 [Member] | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| Small-Mid Cap Core Fund Class R6 [Member] | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| Small-Mid Cap Core Fund Class R6 [Member] | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| Small-Mid Cap Core Fund Class R6 [Member] | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| Small-Mid Cap Core Fund Class R6 [Member] | Public utility [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Small-Mid Cap Core Fund Class R6 [Member] | Financial Support Waived Fee [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.40% |
| C000023543 [Member] | BWX Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| C000023543 [Member] | Carlyle Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| C000023543 [Member] | E.l.f. Beauty, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| C000023543 [Member] | Encompass Health Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| C000023543 [Member] | Freshpet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| C000023543 [Member] | Chemed Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| C000023543 [Member] | Advanced Drainage Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| C000023543 [Member] | Tyler Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| C000023543 [Member] | Brink's Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023543 [Member] | Axon Enterprise, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023542 [Member] | BWX Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| C000023542 [Member] | Carlyle Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| C000023542 [Member] | E.l.f. Beauty, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| C000023542 [Member] | Encompass Health Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| C000023542 [Member] | Freshpet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| C000023542 [Member] | Chemed Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| C000023542 [Member] | Advanced Drainage Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| C000023542 [Member] | Tyler Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| C000023542 [Member] | Brink's Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023542 [Member] | Axon Enterprise, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023542 [Member] | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.60% |
| C000023542 [Member] | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 23.60% |
| C000023542 [Member] | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.80% |
| C000023542 [Member] | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.70% |
| C000023542 [Member] | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000023542 [Member] | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.20% |
| C000023542 [Member] | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.10% |
| C000023542 [Member] | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000023542 [Member] | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| William Blair Small-Mid Cap Growth Fund Class R6 | BWX Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Carlyle Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Small-Mid Cap Growth Fund Class R6 | E.l.f. Beauty, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Encompass Health Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Freshpet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Chemed Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Advanced Drainage Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Tyler Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Brink's Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Axon Enterprise, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.60% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.60% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.80% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.70% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.30% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.20% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.20% |
| William Blair Small-Mid Cap Growth Fund Class R6 | Real Estate Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Qorvo, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Ingredion, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | U.S. Foods Holding Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Taylor Morrison Home Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | ABM Industries, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Commercial Metals Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Tecnoglass, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Healthpeak Properties, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Avnet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | SM Energy Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.90% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.80% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.20% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.80% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.30% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Small-Mid CapValue Fund CLASS I [Member] | Financial Service Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Qorvo, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Ingredion, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | U.S. Foods Holding Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Taylor Morrison Home Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | ABM Industries, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Commercial Metals Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Tecnoglass, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Healthpeak Properties, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Avnet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | SM Energy Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.90% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.80% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.20% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.80% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.30% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Small-Mid Cap Value Fund Class R6 [Member] | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Small Cap Growth Fund Class I | BWX Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Small Cap Growth Fund Class I | Baldwin Insurance Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small Cap Growth Fund Class I | Casella Waste Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Small Cap Growth Fund Class I | E.l.f. Beauty, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small Cap Growth Fund Class I | Encompass Health Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small Cap Growth Fund Class I | Brink's Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Small Cap Growth Fund Class I | Insmed, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Small Cap Growth Fund Class I | Verra Mobility Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Small Cap Growth Fund Class I | Guidewire Software, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small Cap Growth Fund Class I | Skyline Champion Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small Cap Growth Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.70% |
| William Blair Small Cap Growth Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.70% |
| William Blair Small Cap Growth Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.40% |
| William Blair Small Cap Growth Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.80% |
| William Blair Small Cap Growth Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small Cap Growth Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| William Blair Small Cap Growth Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.90% |
| William Blair Small Cap Growth Fund Class I | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Small Cap Growth Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Small Cap Growth Fund Class I | Financial Service Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Small Cap Growth Fund Class I | Exchange Trade Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| C000023540 [Member] | BWX Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| C000023540 [Member] | Baldwin Insurance Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| C000023540 [Member] | Casella Waste Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| C000023540 [Member] | E.l.f. Beauty, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| C000023540 [Member] | Encompass Health Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| C000023540 [Member] | Brink's Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| C000023540 [Member] | Insmed, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| C000023540 [Member] | Verra Mobility Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023540 [Member] | Guidewire Software, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| C000023540 [Member] | Skyline Champion Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| C000023540 [Member] | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.70% |
| C000023540 [Member] | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.70% |
| C000023540 [Member] | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.40% |
| C000023540 [Member] | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.80% |
| C000023540 [Member] | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| C000023540 [Member] | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| C000023540 [Member] | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.90% |
| C000023540 [Member] | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023540 [Member] | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| C000023540 [Member] | Financial Service Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| C000023540 [Member] | Exchange Trade Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| William Blair Small Cap Growth Fund Class R6 | BWX Technologies, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Small Cap Growth Fund Class R6 | Baldwin Insurance Group, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small Cap Growth Fund Class R6 | Casella Waste Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Small Cap Growth Fund Class R6 | E.l.f. Beauty, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small Cap Growth Fund Class R6 | Encompass Health Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small Cap Growth Fund Class R6 | Brink's Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Small Cap Growth Fund Class R6 | Insmed, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Small Cap Growth Fund Class R6 | Verra Mobility Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Small Cap Growth Fund Class R6 | Guidewire Software, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small Cap Growth Fund Class R6 | Skyline Champion Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Small Cap Growth Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.70% |
| William Blair Small Cap Growth Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.70% |
| William Blair Small Cap Growth Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.40% |
| William Blair Small Cap Growth Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.80% |
| William Blair Small Cap Growth Fund Class R6 | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Small Cap Growth Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small Cap Growth Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| William Blair Small Cap Growth Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.90% |
| William Blair Small Cap Growth Fund Class R6 | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Small Cap Growth Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.10% |
| William Blair Small Cap Growth Fund Class R6 | Exchange Trade Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| William Blair Small Cap Value Fund Class I | Taylor Morrison Home Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class I | ABM Industries, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class I | SM Energy Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class I | Expro Group Holdings NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small Cap Value Fund Class I | Verint Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small Cap Value Fund Class I | Kite Realty Group Trust [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class I | Granite Construction, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class I | John Wiley & Sons, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class I | Tri Pointe Homes, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class I | Cal-Maine Foods, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| William Blair Small Cap Value Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.40% |
| William Blair Small Cap Value Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| William Blair Small Cap Value Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| William Blair Small Cap Value Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| William Blair Small Cap Value Fund Class I | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.30% |
| William Blair Small Cap Value Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| William Blair Small Cap Value Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small Cap Value Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.70% |
| William Blair Small Cap Value Fund Class I | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.40% |
| William Blair Small Cap Value Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class I | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Small Cap Value Fund Class N | Taylor Morrison Home Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class N | ABM Industries, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class N | SM Energy Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class N | Expro Group Holdings NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small Cap Value Fund Class N | Verint Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small Cap Value Fund Class N | Kite Realty Group Trust [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class N | Granite Construction, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class N | John Wiley & Sons, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class N | Tri Pointe Homes, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class N | Cal-Maine Foods, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| William Blair Small Cap Value Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| William Blair Small Cap Value Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| William Blair Small Cap Value Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.40% |
| William Blair Small Cap Value Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.70% |
| William Blair Small Cap Value Fund Class N | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Small Cap Value Fund Class N | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| William Blair Small Cap Value Fund Class N | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| William Blair Small Cap Value Fund Class N | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small Cap Value Fund Class N | Financial Service Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.40% |
| William Blair Small Cap Value Fund Class N | Real Estate Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.30% |
| William Blair Small Cap Value Fund Class R6 | Taylor Morrison Home Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class R6 | ABM Industries, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class R6 | SM Energy Co. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class R6 | Expro Group Holdings NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Small Cap Value Fund Class R6 | Verint Systems, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Small Cap Value Fund Class R6 | Kite Realty Group Trust [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class R6 | Granite Construction, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class R6 | John Wiley & Sons, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class R6 | Tri Pointe Homes, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class R6 | Cal-Maine Foods, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| William Blair Small Cap Value Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| William Blair Small Cap Value Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| William Blair Small Cap Value Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.40% |
| William Blair Small Cap Value Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.70% |
| William Blair Small Cap Value Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Small Cap Value Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Small Cap Value Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| William Blair Small Cap Value Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| William Blair Small Cap Value Fund Class R6 | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Small Cap Value Fund Class R6 | Financial Service Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.40% |
| William Blair Small Cap Value Fund Class R6 | Real Estate Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.30% |
| William Blair Global Leaders Fund Class I | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| William Blair Global Leaders Fund Class I | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Global Leaders Fund Class I | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Global Leaders Fund Class I | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Global Leaders Fund Class I | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Global Leaders Fund Class I | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Global Leaders Fund Class I | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Global Leaders Fund Class I | Meta Platforms, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Global Leaders Fund Class I | Atlas Copco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Global Leaders Fund Class I | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Global Leaders Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.70% |
| William Blair Global Leaders Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.90% |
| William Blair Global Leaders Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.30% |
| William Blair Global Leaders Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.80% |
| William Blair Global Leaders Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair Global Leaders Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.90% |
| William Blair Global Leaders Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| William Blair Global Leaders Fund Class I | Financial Services [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Global Leaders Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| William Blair Global Leaders Fund Class I | Public utility [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| William Blair Global Leaders Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.30% |
| William Blair Global Leaders Fund Class I | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| William Blair Global Leaders Fund Class I | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| William Blair Global Leaders Fund Class I | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 56.50% |
| William Blair Global Leaders Fund Class I | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 26.90% |
| William Blair Global Leaders Fund Class N | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| William Blair Global Leaders Fund Class N | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Global Leaders Fund Class N | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Global Leaders Fund Class N | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Global Leaders Fund Class N | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Global Leaders Fund Class N | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Global Leaders Fund Class N | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Global Leaders Fund Class N | Meta Platforms, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Global Leaders Fund Class N | Atlas Copco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Global Leaders Fund Class N | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Global Leaders Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.70% |
| William Blair Global Leaders Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.90% |
| William Blair Global Leaders Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.30% |
| William Blair Global Leaders Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.80% |
| William Blair Global Leaders Fund Class N | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Global Leaders Fund Class N | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair Global Leaders Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.90% |
| William Blair Global Leaders Fund Class N | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| William Blair Global Leaders Fund Class N | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| William Blair Global Leaders Fund Class N | Public utility [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| William Blair Global Leaders Fund Class N | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.30% |
| William Blair Global Leaders Fund Class N | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.40% |
| William Blair Global Leaders Fund Class N | JAPAN | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| William Blair Global Leaders Fund Class N | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56.50% |
| William Blair Global Leaders Fund Class N | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 26.90% |
| William Blair Global Leaders Fund Class R6 | Microsoft Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| William Blair Global Leaders Fund Class R6 | Amazon.com, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Global Leaders Fund Class R6 | Alphabet, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Global Leaders Fund Class R6 | NVIDIA Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Global Leaders Fund Class R6 | Mastercard, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Global Leaders Fund Class R6 | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Global Leaders Fund Class R6 | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.20% |
| William Blair Global Leaders Fund Class R6 | Meta Platforms, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Global Leaders Fund Class R6 | Atlas Copco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Global Leaders Fund Class R6 | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Global Leaders Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.70% |
| William Blair Global Leaders Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.90% |
| William Blair Global Leaders Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.30% |
| William Blair Global Leaders Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.80% |
| William Blair Global Leaders Fund Class R6 | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Global Leaders Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair Global Leaders Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.90% |
| William Blair Global Leaders Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| William Blair Global Leaders Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| William Blair Global Leaders Fund Class R6 | Public utility [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| William Blair Global Leaders Fund Class R6 | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.30% |
| William Blair Global Leaders Fund Class R6 | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| William Blair Global Leaders Fund Class R6 | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| William Blair Global Leaders Fund Class R6 | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 56.50% |
| William Blair Global Leaders Fund Class R6 | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 26.90% |
| William Blair International Leaders Fund Class I | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| William Blair International Leaders Fund Class I | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| William Blair International Leaders Fund Class I | Atlas Copco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair International Leaders Fund Class I | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| William Blair International Leaders Fund Class I | Tokyo Electron Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class I | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class I | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair International Leaders Fund Class I | ICON PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair International Leaders Fund Class I | London Stock Exchange Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair International Leaders Fund Class I | Hoya Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair International Leaders Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 28.30% |
| William Blair International Leaders Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.50% |
| William Blair International Leaders Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.50% |
| William Blair International Leaders Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.30% |
| William Blair International Leaders Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| William Blair International Leaders Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair International Leaders Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair International Leaders Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair International Leaders Fund Class I | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.40% |
| William Blair International Leaders Fund Class I | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| William Blair International Leaders Fund Class I | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.70% |
| William Blair International Leaders Fund Class I | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| William Blair International Leaders Fund Class I | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 43.20% |
| William Blair International Leaders Fund Class N | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| William Blair International Leaders Fund Class N | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| William Blair International Leaders Fund Class N | Atlas Copco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair International Leaders Fund Class N | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| William Blair International Leaders Fund Class N | Tokyo Electron Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class N | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class N | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair International Leaders Fund Class N | ICON PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair International Leaders Fund Class N | London Stock Exchange Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair International Leaders Fund Class N | Hoya Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair International Leaders Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 28.30% |
| William Blair International Leaders Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.50% |
| William Blair International Leaders Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.50% |
| William Blair International Leaders Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.30% |
| William Blair International Leaders Fund Class N | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| William Blair International Leaders Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair International Leaders Fund Class N | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair International Leaders Fund Class N | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair International Leaders Fund Class N | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class N | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.40% |
| William Blair International Leaders Fund Class N | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| William Blair International Leaders Fund Class N | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.70% |
| William Blair International Leaders Fund Class N | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| William Blair International Leaders Fund Class N | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 43.20% |
| William Blair International Leaders Fund Class R6 | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| William Blair International Leaders Fund Class R6 | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| William Blair International Leaders Fund Class R6 | Atlas Copco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair International Leaders Fund Class R6 | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| William Blair International Leaders Fund Class R6 | Tokyo Electron Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class R6 | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class R6 | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair International Leaders Fund Class R6 | ICON PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| William Blair International Leaders Fund Class R6 | London Stock Exchange Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair International Leaders Fund Class R6 | Hoya Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair International Leaders Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 28.30% |
| William Blair International Leaders Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.50% |
| William Blair International Leaders Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.50% |
| William Blair International Leaders Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 19.30% |
| William Blair International Leaders Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair International Leaders Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair International Leaders Fund Class R6 | Financial Services [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.30% |
| William Blair International Leaders Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair International Leaders Fund Class R6 | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Leaders Fund Class R6 | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.40% |
| William Blair International Leaders Fund Class R6 | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| William Blair International Leaders Fund Class R6 | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.70% |
| William Blair International Leaders Fund Class R6 | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| William Blair International Leaders Fund Class R6 | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 43.20% |
| William Blair International Growth Fund Class I | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.60% |
| William Blair International Growth Fund Class I | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Growth Fund Class I | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Growth Fund Class I | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class I | London Stock Exchange Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class I | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair International Growth Fund Class I | Three i Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class I | Keyence Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class I | Tokio Marine Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class I | SAP SE [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 25.30% |
| William Blair International Growth Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.10% |
| William Blair International Growth Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.60% |
| William Blair International Growth Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 25.30% |
| William Blair International Growth Fund Class I | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.70% |
| William Blair International Growth Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Growth Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| William Blair International Growth Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair International Growth Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair International Growth Fund Class I | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| William Blair International Growth Fund Class I | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Growth Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.80% |
| William Blair International Growth Fund Class I | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| William Blair International Growth Fund Class I | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.90% |
| William Blair International Growth Fund Class I | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair International Growth Fund Class I | Asia EX Japan [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair International Growth Fund Class I | Europe Ex U.K. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 38.80% |
| William Blair International Growth Fund Class N | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.60% |
| William Blair International Growth Fund Class N | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Growth Fund Class N | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Growth Fund Class N | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class N | London Stock Exchange Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class N | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair International Growth Fund Class N | Three i Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class N | Keyence Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class N | Tokio Marine Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class N | SAP SE [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 25.30% |
| William Blair International Growth Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| William Blair International Growth Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.60% |
| William Blair International Growth Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 25.30% |
| William Blair International Growth Fund Class N | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.70% |
| William Blair International Growth Fund Class N | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| William Blair International Growth Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| William Blair International Growth Fund Class N | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| William Blair International Growth Fund Class N | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| William Blair International Growth Fund Class N | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| William Blair International Growth Fund Class N | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| William Blair International Growth Fund Class N | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| William Blair International Growth Fund Class N | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| William Blair International Growth Fund Class N | JAPAN | |
| Holdings [Line Items] | |
| Percent of Total Investments | 16.90% |
| William Blair International Growth Fund Class N | Europe [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 38.80% |
| William Blair International Growth Fund Class N | Americas [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.10% |
| William Blair International Growth Fund Class N | Asia Pacific [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| William Blair International Growth Fund Class R6 | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.60% |
| William Blair International Growth Fund Class R6 | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Growth Fund Class R6 | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Growth Fund Class R6 | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class R6 | London Stock Exchange Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class R6 | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair International Growth Fund Class R6 | Three i Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Growth Fund Class R6 | Keyence Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class R6 | Tokio Marine Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class R6 | SAP SE [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair International Growth Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 25.30% |
| William Blair International Growth Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.10% |
| William Blair International Growth Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.60% |
| William Blair International Growth Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 25.30% |
| William Blair International Growth Fund Class R6 | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.70% |
| William Blair International Growth Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Growth Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| William Blair International Growth Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair International Growth Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair International Growth Fund Class R6 | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair International Growth Fund Class R6 | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.80% |
| William Blair International Growth Fund Class R6 | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| William Blair International Growth Fund Class R6 | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.90% |
| William Blair International Growth Fund Class R6 | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| William Blair International Growth Fund Class R6 | Europe [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 38.80% |
| William Blair International Growth Fund Class R6 | Americas [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair International Growth Fund Class R6 | Asia Pacific [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Institutional International Growth Fund Institutional Class | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.60% |
| William Blair Institutional International Growth Fund Institutional Class | Novo Nordisk AS [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Institutional International Growth Fund Institutional Class | ASML Holding NV [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Institutional International Growth Fund Institutional Class | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Institutional International Growth Fund Institutional Class | London Stock Exchange Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Institutional International Growth Fund Institutional Class | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Institutional International Growth Fund Institutional Class | Three i Group PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Institutional International Growth Fund Institutional Class | Keyence Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Institutional International Growth Fund Institutional Class | Tokio Marine Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Institutional International Growth Fund Institutional Class | SAP SE [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| William Blair Institutional International Growth Fund Institutional Class | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 25.30% |
| William Blair Institutional International Growth Fund Institutional Class | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.20% |
| William Blair Institutional International Growth Fund Institutional Class | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.70% |
| William Blair Institutional International Growth Fund Institutional Class | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 25.30% |
| William Blair Institutional International Growth Fund Institutional Class | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.70% |
| William Blair Institutional International Growth Fund Institutional Class | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Institutional International Growth Fund Institutional Class | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| William Blair Institutional International Growth Fund Institutional Class | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Institutional International Growth Fund Institutional Class | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Institutional International Growth Fund Institutional Class | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| William Blair Institutional International Growth Fund Institutional Class | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| William Blair Institutional International Growth Fund Institutional Class | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.80% |
| William Blair Institutional International Growth Fund Institutional Class | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.10% |
| William Blair Institutional International Growth Fund Institutional Class | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.90% |
| William Blair Institutional International Growth Fund Institutional Class | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.20% |
| William Blair Institutional International Growth Fund Institutional Class | Asia EX Japan [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Institutional International Growth Fund Institutional Class | Europe Ex U.K. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 38.90% |
| William Blair International Small Cap Growth Fund Class I | ASPEED Technology, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair International Small Cap Growth Fund Class I | Pro Medicus Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Small Cap Growth Fund Class I | Diploma PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair International Small Cap Growth Fund Class I | North West Co., Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair International Small Cap Growth Fund Class I | Beazley PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair International Small Cap Growth Fund Class I | Lifco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair International Small Cap Growth Fund Class I | Beijer Ref AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair International Small Cap Growth Fund Class I | Hemnet Group AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair International Small Cap Growth Fund Class I | CTS Eventim AG & Co. KGaA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair International Small Cap Growth Fund Class I | D'ieteren Group [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair International Small Cap Growth Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.30% |
| William Blair International Small Cap Growth Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| William Blair International Small Cap Growth Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.90% |
| William Blair International Small Cap Growth Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.30% |
| William Blair International Small Cap Growth Fund Class I | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.60% |
| William Blair International Small Cap Growth Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.40% |
| William Blair International Small Cap Growth Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| William Blair International Small Cap Growth Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Small Cap Growth Fund Class I | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| William Blair International Small Cap Growth Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| William Blair International Small Cap Growth Fund Class I | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair International Small Cap Growth Fund Class I | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| William Blair International Small Cap Growth Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.60% |
| William Blair International Small Cap Growth Fund Class I | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| William Blair International Small Cap Growth Fund Class I | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21% |
| William Blair International Small Cap Growth Fund Class I | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.60% |
| William Blair International Small Cap Growth Fund Class I | Asia EX Japan [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.60% |
| William Blair International Small Cap Growth Fund Class I | Europe Ex U.K. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 31.20% |
| C000023525 [Member] | ASPEED Technology, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023525 [Member] | Pro Medicus Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| C000023525 [Member] | Diploma PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| C000023525 [Member] | North West Co., Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| C000023525 [Member] | Beazley PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| C000023525 [Member] | Lifco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| C000023525 [Member] | Beijer Ref AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| C000023525 [Member] | Hemnet Group AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023525 [Member] | CTS Eventim AG & Co. KGaA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| C000023525 [Member] | D'ieteren Group [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| C000023525 [Member] | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.30% |
| C000023525 [Member] | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| C000023525 [Member] | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.90% |
| C000023525 [Member] | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.30% |
| C000023525 [Member] | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.60% |
| C000023525 [Member] | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.40% |
| C000023525 [Member] | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| C000023525 [Member] | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| C000023525 [Member] | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| C000023525 [Member] | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| C000023525 [Member] | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| C000023525 [Member] | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.60% |
| C000023525 [Member] | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| C000023525 [Member] | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21% |
| C000023525 [Member] | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.60% |
| C000023525 [Member] | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| C000023525 [Member] | Asia EX Japan [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.60% |
| C000023525 [Member] | Europe Ex U.K. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 31.20% |
| William Blair International Small Cap Growth Fund Class R6 | ASPEED Technology, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair International Small Cap Growth Fund Class R6 | Pro Medicus Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair International Small Cap Growth Fund Class R6 | Diploma PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair International Small Cap Growth Fund Class R6 | North West Co., Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair International Small Cap Growth Fund Class R6 | Beazley PLC [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair International Small Cap Growth Fund Class R6 | Lifco AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair International Small Cap Growth Fund Class R6 | Beijer Ref AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair International Small Cap Growth Fund Class R6 | Hemnet Group AB [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair International Small Cap Growth Fund Class R6 | CTS Eventim AG & Co. KGaA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair International Small Cap Growth Fund Class R6 | D'ieteren Group [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair International Small Cap Growth Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 23.30% |
| William Blair International Small Cap Growth Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.30% |
| William Blair International Small Cap Growth Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.90% |
| William Blair International Small Cap Growth Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.30% |
| William Blair International Small Cap Growth Fund Class R6 | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.60% |
| William Blair International Small Cap Growth Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.40% |
| William Blair International Small Cap Growth Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| William Blair International Small Cap Growth Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair International Small Cap Growth Fund Class R6 | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| William Blair International Small Cap Growth Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| William Blair International Small Cap Growth Fund Class R6 | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| William Blair International Small Cap Growth Fund Class R6 | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 20.60% |
| William Blair International Small Cap Growth Fund Class R6 | UNITED KINGDOM | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| William Blair International Small Cap Growth Fund Class R6 | JAPAN | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21% |
| William Blair International Small Cap Growth Fund Class R6 | Western Hemisphere [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.60% |
| William Blair International Small Cap Growth Fund Class R6 | European Union [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 31.20% |
| William Blair International Small Cap Growth Fund Class R6 | Asia Pacific [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.60% |
| William Blair International Small Cap Growth Fund Class R6 | Africa [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Leaders Fund Class I | Tencent Holdings Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.30% |
| William Blair Emerging Markets Leaders Fund Class I | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| William Blair Emerging Markets Leaders Fund Class I | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Emerging Markets Leaders Fund Class I | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Emerging Markets Leaders Fund Class I | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| William Blair Emerging Markets Leaders Fund Class I | Kotak Mahindra Bank Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Emerging Markets Leaders Fund Class I | WEG SA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| William Blair Emerging Markets Leaders Fund Class I | SK Hynix, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Leaders Fund Class I | MercadoLibre, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Emerging Markets Leaders Fund Class I | Bank Central Asia Tbk. PT [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Leaders Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 39% |
| William Blair Emerging Markets Leaders Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| William Blair Emerging Markets Leaders Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.20% |
| William Blair Emerging Markets Leaders Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.20% |
| William Blair Emerging Markets Leaders Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.30% |
| William Blair Emerging Markets Leaders Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.50% |
| William Blair Emerging Markets Leaders Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| William Blair Emerging Markets Leaders Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Leaders Fund Class I | Financial Support Waived Fee [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.70% |
| William Blair Emerging Markets Leaders Fund Class I | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.80% |
| William Blair Emerging Markets Leaders Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 89% |
| William Blair Emerging Markets Leaders Fund Class I | Europe [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.90% |
| William Blair Emerging Markets Leaders Fund Class N | Tencent Holdings Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.30% |
| William Blair Emerging Markets Leaders Fund Class N | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| William Blair Emerging Markets Leaders Fund Class N | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Emerging Markets Leaders Fund Class N | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Emerging Markets Leaders Fund Class N | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| William Blair Emerging Markets Leaders Fund Class N | Kotak Mahindra Bank Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Emerging Markets Leaders Fund Class N | WEG SA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| William Blair Emerging Markets Leaders Fund Class N | SK Hynix, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Leaders Fund Class N | MercadoLibre, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Emerging Markets Leaders Fund Class N | Bank Central Asia Tbk. PT [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Leaders Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 39% |
| William Blair Emerging Markets Leaders Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| William Blair Emerging Markets Leaders Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.20% |
| William Blair Emerging Markets Leaders Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.20% |
| William Blair Emerging Markets Leaders Fund Class N | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.30% |
| William Blair Emerging Markets Leaders Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.50% |
| William Blair Emerging Markets Leaders Fund Class N | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| William Blair Emerging Markets Leaders Fund Class N | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Leaders Fund Class N | Financial Service Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.70% |
| William Blair Emerging Markets Leaders Fund Class N | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.80% |
| William Blair Emerging Markets Leaders Fund Class N | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 89% |
| William Blair Emerging Markets Leaders Fund Class N | Europe [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.90% |
| William Blair Emerging Markets Leaders Fund Class R6 | Tencent Holdings Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.30% |
| William Blair Emerging Markets Leaders Fund Class R6 | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| William Blair Emerging Markets Leaders Fund Class R6 | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Emerging Markets Leaders Fund Class R6 | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Emerging Markets Leaders Fund Class R6 | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| William Blair Emerging Markets Leaders Fund Class R6 | Kotak Mahindra Bank Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| William Blair Emerging Markets Leaders Fund Class R6 | WEG SA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| William Blair Emerging Markets Leaders Fund Class R6 | SK Hynix, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Leaders Fund Class R6 | MercadoLibre, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.60% |
| William Blair Emerging Markets Leaders Fund Class R6 | Bank Central Asia Tbk. PT [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Leaders Fund Class R6 | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 39% |
| William Blair Emerging Markets Leaders Fund Class R6 | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| William Blair Emerging Markets Leaders Fund Class R6 | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 15.20% |
| William Blair Emerging Markets Leaders Fund Class R6 | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.20% |
| William Blair Emerging Markets Leaders Fund Class R6 | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| William Blair Emerging Markets Leaders Fund Class R6 | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.50% |
| William Blair Emerging Markets Leaders Fund Class R6 | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| William Blair Emerging Markets Leaders Fund Class R6 | Financial Services [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.70% |
| William Blair Emerging Markets Leaders Fund Class R6 | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| William Blair Emerging Markets Leaders Fund Class R6 | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| William Blair Emerging Markets Leaders Fund Class R6 | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| William Blair Emerging Markets Leaders Fund Class R6 | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 89% |
| William Blair Emerging Markets Growth Fund Class I | Tencent Holdings Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| William Blair Emerging Markets Growth Fund Class I | PDD Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Growth Fund Class I | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.80% |
| William Blair Emerging Markets Growth Fund Class I | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Emerging Markets Growth Fund Class I | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund Class I | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Emerging Markets Growth Fund Class I | SK Hynix, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| William Blair Emerging Markets Growth Fund Class I | MercadoLibre, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund Class I | Bank Central Asia Tbk. PT [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund Class I | NTPC Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets Growth Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.90% |
| William Blair Emerging Markets Growth Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| William Blair Emerging Markets Growth Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.50% |
| William Blair Emerging Markets Growth Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.60% |
| William Blair Emerging Markets Growth Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| William Blair Emerging Markets Growth Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Emerging Markets Growth Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| William Blair Emerging Markets Growth Fund Class I | Financial Services [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.90% |
| William Blair Emerging Markets Growth Fund Class I | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Emerging Markets Growth Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| William Blair Emerging Markets Growth Fund Class I | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets Growth Fund Class I | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair Emerging Markets Growth Fund Class I | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.40% |
| William Blair Emerging Markets Growth Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 84% |
| William Blair Emerging Markets Growth Fund Class N | Tencent Holdings Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| William Blair Emerging Markets Growth Fund Class N | PDD Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Growth Fund Class N | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.80% |
| William Blair Emerging Markets Growth Fund Class N | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Emerging Markets Growth Fund Class N | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund Class N | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Emerging Markets Growth Fund Class N | SK Hynix, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| William Blair Emerging Markets Growth Fund Class N | MercadoLibre, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund Class N | Bank Central Asia Tbk. PT [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund Class N | NTPC Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets Growth Fund Class N | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.90% |
| William Blair Emerging Markets Growth Fund Class N | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| William Blair Emerging Markets Growth Fund Class N | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.50% |
| William Blair Emerging Markets Growth Fund Class N | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.60% |
| William Blair Emerging Markets Growth Fund Class N | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.90% |
| William Blair Emerging Markets Growth Fund Class N | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| William Blair Emerging Markets Growth Fund Class N | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Emerging Markets Growth Fund Class N | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| William Blair Emerging Markets Growth Fund Class N | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Emerging Markets Growth Fund Class N | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| William Blair Emerging Markets Growth Fund Class N | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets Growth Fund Class N | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair Emerging Markets Growth Fund Class N | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.40% |
| William Blair Emerging Markets Growth Fund Class N | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 84% |
| William Blair Emerging Markets Growth Fund (Class R6) | Tencent Holdings Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| William Blair Emerging Markets Growth Fund (Class R6) | PDD Holdings, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Growth Fund (Class R6) | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.80% |
| William Blair Emerging Markets Growth Fund (Class R6) | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Emerging Markets Growth Fund (Class R6) | Reliance Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund (Class R6) | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| William Blair Emerging Markets Growth Fund (Class R6) | SK Hynix, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| William Blair Emerging Markets Growth Fund (Class R6) | MercadoLibre, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund (Class R6) | Bank Central Asia Tbk. PT [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets Growth Fund (Class R6) | NTPC Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets Growth Fund (Class R6) | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30.90% |
| William Blair Emerging Markets Growth Fund (Class R6) | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.40% |
| William Blair Emerging Markets Growth Fund (Class R6) | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.50% |
| William Blair Emerging Markets Growth Fund (Class R6) | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.60% |
| William Blair Emerging Markets Growth Fund (Class R6) | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.90% |
| William Blair Emerging Markets Growth Fund (Class R6) | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| William Blair Emerging Markets Growth Fund (Class R6) | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.10% |
| William Blair Emerging Markets Growth Fund (Class R6) | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.80% |
| William Blair Emerging Markets Growth Fund (Class R6) | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| William Blair Emerging Markets Growth Fund (Class R6) | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets Growth Fund (Class R6) | Real Estate Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Emerging Markets Growth Fund (Class R6) | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair Emerging Markets Growth Fund (Class R6) | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.40% |
| William Blair Emerging Markets Growth Fund (Class R6) | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 84% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Dixon Technologies India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | ABB India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.30% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | SK Hynix, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.80% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | MercadoLibre, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Bank Central Asia Tbk. PT [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Trent Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | HD Hyundai Electric Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 36.60% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.60% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.80% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.80% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.90% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.30% |
| William Blair Emerging Markets ex China Growth Fund (Class I) | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 77% |
| William Blair Emerging Markets ex China Growth Fund | Dixon Technologies India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Emerging Markets ex China Growth Fund | ABB India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Emerging Markets ex China Growth Fund | Taiwan Semiconductor Manufacturing Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.30% |
| William Blair Emerging Markets ex China Growth Fund | MediaTek, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets ex China Growth Fund | Samsung Electronics Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| William Blair Emerging Markets ex China Growth Fund | SK Hynix, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.80% |
| William Blair Emerging Markets ex China Growth Fund | MercadoLibre, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| William Blair Emerging Markets ex China Growth Fund | Bank Central Asia Tbk. PT [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Emerging Markets ex China Growth Fund | Trent Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Emerging Markets ex China Growth Fund | HD Hyundai Electric Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets ex China Growth Fund | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 36.60% |
| William Blair Emerging Markets ex China Growth Fund | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| William Blair Emerging Markets ex China Growth Fund | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14% |
| William Blair Emerging Markets ex China Growth Fund | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 16.60% |
| William Blair Emerging Markets ex China Growth Fund | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.80% |
| William Blair Emerging Markets ex China Growth Fund | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| William Blair Emerging Markets ex China Growth Fund | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.80% |
| William Blair Emerging Markets ex China Growth Fund | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets ex China Growth Fund | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.90% |
| William Blair Emerging Markets ex China Growth Fund | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.50% |
| William Blair Emerging Markets ex China Growth Fund | Real Estate Others [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4% |
| William Blair Emerging Markets ex China Growth Fund | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| William Blair Emerging Markets ex China Growth Fund | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.30% |
| William Blair Emerging Markets ex China Growth Fund | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 77% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | ASPEED Technology, Inc. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Dixon Technologies India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | KEI Industries Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | ABB India Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Wiwynn Corp. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Lotes Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Asia Vital Components Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Godrej Properties Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Huaming Power Equipment Co. Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Macrotech Developers Ltd. [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 15.60% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 31.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Communications Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.70% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.80% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.90% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | EMEA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Latin America [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.30% |
| William Blair Emerging Markets Small Cap Growth Fund Class I | Asia [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 81.50% |
