Summary of Valuation and Qualifying Accounts (Parenthetical) (Detail) $ in Millions	12 Months Ended
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

Adjustments in discount provision due to cumulative effect of retained earnings and deferred revenue.

No definition available.

Name:	sam_AdjustmentsInDiscountProvisionDueToCumulativeEffectOfRetainedEarningsAndDeferredRevenue
Namespace Prefix:	sam_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration