Third-Party Production Prepayments (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 27, 2021	Dec. 26, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Percentage of brews and packages	57.00%
Total third-party production prepayments	$ 93,243	$ 56,843
Payments for capital improvements	10,000
Additional payment for accessing facility	17,900
Contractual shortfall fees	67,600
Reclassification of third-party prepayments from current assets to non-current assets	$ 14,800

Additional payment for accessing facility.

No definition available.

Name:	sam_AdditionalPaymentForAccessingFacility
Namespace Prefix:	sam_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Contractual shortfall fees.

+ References

No definition available.

+ Details

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

- Definition

Percentage of brews and packages.

+ References

No definition available.

+ Details

Name:	sam_PercentageOfBrewsAndPackages
Namespace Prefix:	sam_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reclassification of prepaid expenses from current assets to non-current assets.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

Name:	us-gaap_DeferredCostsCapitalizedPrepaidAndOtherAssetsDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow for acquisition of or capital improvements to properties held for investment (operating, managed, leased) or for use.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsForCapitalImprovements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Sum of the carrying amounts as of the balance sheet date of amounts paid in advance for expenses which will be charged against earnings in periods after one year or beyond the operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_PrepaidExpenseNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant