Document and Entity Information - shares
6 Months Ended
Jun. 29, 2019
Jul. 20, 2019
Document Information [Line Items]    
Document Quarterly Report true  
Document Transition Report false  
Document Type 10-Q  
Document Period End Date Jun. 29, 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 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 Q2  
Entity Central Index Key 0000949870  
Current Fiscal Year End Date --12-29  
Common Class A    
Document Information [Line Items]    
Trading Symbol SAM  
Entity Common Stock, Shares Outstanding   9,185,036
Title of 12(b) Security Common Stock  
Security Exchange Name NYSE  
Common Class B    
Document Information [Line Items]    
No Trading Symbol Flag true  
Entity Common Stock, Shares Outstanding   2,917,983
Title of 12(b) Security Common Stock