2.4.0.6 Html 7 42 1 true 7 0 false 2 false false R1.htm 000000 - Document - Document and Entity Information Sheet http://www.williamblairfunds.com/role/DocumentDocumentandEntityInformation Document and Entity Information false true R2.htm 000011 - Document - Risk/Return Summary {Unlabeled} - William Blair International Leaders Fund (Class N Shares) Sheet http://www.williamblairfunds.com/role/DocumentRiskReturnSummaryUnlabeledWilliamBlairInternationalLeadersFundClassNShares Risk/Return Summary - William Blair International Leaders Fund (Class N Shares) false false R6.htm 000019 - Disclosure - Risk/Return Detail Data {Elements} - William Blair International Leaders Fund (Class N Shares) Sheet http://www.williamblairfunds.com/role/DisclosureRiskReturnDetailDataElementsWilliamBlairInternationalLeadersFundClassNShares Risk/Return Detail Data - William Blair International Leaders Fund (Class N Shares) false true R7.htm 000021 - Document - Risk/Return Summary {Unlabeled} - William Blair International Leaders Fund (Class I Shares) Sheet http://www.williamblairfunds.com/role/DocumentRiskReturnSummaryUnlabeledWilliamBlairInternationalLeadersFundClassIShares Risk/Return Summary - William Blair International Leaders Fund (Class I Shares) false false R11.htm 000029 - Disclosure - Risk/Return Detail Data {Elements} - William Blair International Leaders Fund (Class I Shares) Sheet http://www.williamblairfunds.com/role/DisclosureRiskReturnDetailDataElementsWilliamBlairInternationalLeadersFundClassIShares Risk/Return Detail Data - William Blair International Leaders Fund (Class I Shares) false true R12.htm 000031 - Document - Risk/Return Summary {Unlabeled} - William Blair International Leaders Fund (Institutional Class) Sheet http://www.williamblairfunds.com/role/DocumentRiskReturnSummaryUnlabeledWilliamBlairInternationalLeadersFundInstitutionalClass Risk/Return Summary - William Blair International Leaders Fund (Institutional Class) false false R16.htm 000039 - Disclosure - Risk/Return Detail Data {Elements} - William Blair International Leaders Fund (Institutional Class) Sheet http://www.williamblairfunds.com/role/DisclosureRiskReturnDetailDataElementsWilliamBlairInternationalLeadersFundInstitutionalClass Risk/Return Detail Data - William Blair International Leaders Fund (Institutional Class) false false R17.htm 040000 - Disclosure - Risk/Return Detail Data {Elements} Sheet http://xbrl.sec.gov/rr/role/RiskReturnDetailData Risk/Return Detail Data true false All Reports Book All Reports wbf-20120815.xml wbf-20120815.xsd wbf-20120815_cal.xml wbf-20120815_def.xml wbf-20120815_lab.xml wbf-20120815_pre.xml true true