v3.10.0.1
Document and Entity Information - shares
6 Months Ended
Jun. 30, 2018
Jul. 20, 2018
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2  
Trading Symbol SAM  
Entity Registrant Name BOSTON BEER CO INC  
Entity Central Index Key 0000949870  
Current Fiscal Year End Date --12-30  
Entity Filer Category Large Accelerated Filer  
Common Class A    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   8,733,767
Common Class B    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   3,017,983