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v3.20.4

Summary of Valuation and Qualifying Accounts (Parenthetical) (Detail) $ in Millions | 12 Months Ended
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Dec. 29, 2018 USD ($)
Valuation And Qualifying Accounts [Abstract] |
Cumulative effect adjustment to retained earnings and the current year adjustment to deferred revenue | $ 1.7

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- Definition Adjustments in discount provision due to cumulative effect of retained earnings and deferred revenue. + References No definition available. + Details
Name: | sam_AdjustmentsInDiscountProvisionDueToCumulativeEffectOfRetainedEarningsAndDeferredRevenue
Namespace Prefix: | sam_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | srt_ValuationAndQualifyingAccountsAbstract
Namespace Prefix: | srt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration