v3.10.0.1
Document And Entity Information - USD ($)
$ in Millions
12 Months Ended
Dec. 29, 2018
Feb. 15, 2019
Jun. 30, 2018
Document Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 29, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Entity Registrant Name BOSTON BEER CO INC    
Entity Central Index Key 0000949870    
Current Fiscal Year End Date --12-29    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 2,473.7
Trading Symbol SAM    
Entity Shell Company false    
Entity Emerging Growth Company false    
Entity Small Business false    
Common Class A      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   8,706,975  
Common Class B      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   2,917,983