Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 28, 2019	Feb. 14, 2020	Jun. 29, 2019
Document Information [Line Items]
Document Annual Report	true
Document Transition Report	false
Document Type	10-K
Document Period End Date	Dec. 28, 2019
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Registrant Name	BOSTON BEER CO INC
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Small Business	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 3,163.5
Entity Emerging Growth Company	false
Entity File Number	1-14092
Entity Incorporation, State or Country Code	MA
Entity Tax Identification Number	04-3284048
Entity Address, Address Line One	One Design Center Place, Suite 850
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02210
City Area Code	617
Local Phone Number	368-5000
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0000949870
Current Fiscal Year End Date	--12-28
Trading Symbol	SAM
Security Exchange Name	NYSE
Title of 12(b) Security	Class A Common Stock
Common Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		9,481,434
Common Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		2,672,983