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Marketable Securities - Reconciles Cost Basis to Fair Market Value of Company's Equity Security (Detail) (Equity securities, USD $)
In Millions, unless otherwise specified
Dec. 27, 2014
Sep. 27, 2014
Equity securities
    
Schedule Of Marketable Securities [Line Items]    
Cost $ 15.5us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 $ 15.5us-gaap_AvailableForSaleSecuritiesEquitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Gross Unrealized Gains 19.7holx_AvailableForSaleSecuritiesGrossUnrealizedGainOne
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 10.2holx_AvailableForSaleSecuritiesGrossUnrealizedGainOne
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Gross Unrealized Losses (5.7)holx_AvailableForSaleSecuritiesGrossUnrealizedLossesTwo
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 (1.3)holx_AvailableForSaleSecuritiesGrossUnrealizedLossesTwo
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember
Fair Value $ 29.5us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 $ 24.4us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember