| Document and Entity Information | Jul. 03, 2019 |
| Cover [Abstract] | |
| Entity Registrant Name | BOSTON BEER CO INC |
| Amendment Flag | false |
| Entity Central Index Key | 0000949870 |
| Document Type | 8-K/A |
| Document Period End Date | Jul. 3, 2019 |
| Entity Incorporation State Country Code | MA |
| Entity File Number | 001-14092 |
| Entity Tax Identification Number | 04-3284048 |
| Entity Address, Address Line One | One Design Center Place |
| Entity Address, Address Line Two | 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Class A Common Stock. $0.01 par value |
| Trading Symbol | SAM |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
