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Label Element Value
Prospectus [Line Items] rr_ProspectusLineItems  
Document Type dei_DocumentType 497
Document Period End Date dei_DocumentPeriodEndDate Sep. 30, 2018
Entity Registrant Name dei_EntityRegistrantName FMI FUNDS INC
Entity Central Index Key dei_EntityCentralIndexKey 0001023391
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Aug. 12, 2019
Document Effective Date dei_DocumentEffectiveDate Aug. 12, 2019
Prospectus Date rr_ProspectusDate Aug. 12, 2019
Entity Inv Company Type dei_EntityInvCompanyType N-1A
Common Stock Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Common Stock Fund
Supplement to Prospectus [Text Block] rr_SupplementToProspectusTextBlock
FMI Funds, Inc.
FMI Common Stock Fund
Investor Class (Ticker Symbol: FMIMX)
Institutional Class (Ticker Symbol: FMIUX)
August 12, 2019
Supplement to the Summary Prospectuses and Prospectus, each dated January 31, 2019

This supplement serves as notification that, effective immediately, the sentence directly following the bar chart entitled “Annual Returns” in the subsection entitled “FMI Common Stock Fund Summary – Performance” is deleted and replaced with the following:
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the ten year period shown on the bar chart, the highest total return for the Fund’s Investor Class shares for a quarter was 21.52% (quarter ended June 30, 2009) and the lowest total return for a quarter was -16.31% (quarter ended September 30, 2011).
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest total return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.52%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest total return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (16.31%)
Supplement Closing [Text Block] ck0001023391_SupplementClosingTextBlock
The date of this supplement is August 12, 2019.

Please retain this supplement for reference.
Common Stock Fund | Common Stock Fund Investor Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol FMIMX
Common Stock Fund | Common Stock Fund Institutional Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol FMIUX