Employee Retirement Plans - Additional Information (Detail)		1 Months Ended	12 Months Ended
	Dec. 29, 2019	Apr. 30, 2019 USD ($)	Dec. 28, 2019 USD ($) CompensationPlan	Dec. 29, 2018 USD ($)	Dec. 30, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assumed average annual returns on assets			1.75%
Money market funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Securities target allocation			100.00%
Retiree Medical Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded projected pension benefits			$ 888,000	$ 731,000
Pension Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded projected pension benefits			$ 2,734,000	$ 2,035,000
Benefit obligation, discount rate			3.32%	4.27%
Union Number 1199 Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated cost of termination of retirement pension plan		$ 1,900,000
Non-Union Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of retirement plans | CompensationPlan			1
Non-Union Plans | Boston Beer 401 (k) Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Eligibility timing			eligible to participate in the Plan immediately upon employment.
Voluntary contributions of annual compensation			60.00%
Employer matching contribution percentage			6.00%
Contributions Plan			$ 4,000,000.0	$ 3,500,000	$ 3,200,000
Non-Union Plans | Boston Beer 401 (k) Plan | Company's match for the first $1,000 of the eligible participants contribute
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer match percentage			100.00%
Contribution amount by the company			$ 1,000
Non-Union Plans | Boston Beer 401 (k) Plan | Company's match thereafter
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer match percentage			50.00%
Non-Union Plans | Boston Beer 401 (k) Plan | Company's match thereafter | Subsequent Event
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contribution percentage	3.00%
Employer match percentage	100.00%
Non-Union Plans | Boston Beer 401 (k) Plan | Company's match for the first 3% of the eligible participants contribute | Subsequent Event
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contribution percentage	5.00%
Employer match percentage	50.00%
Non-Union Plans | Dogfish Head 401 (K) Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Voluntary contributions of annual compensation			60.00%
Employer matching contribution percentage			5.00%
Contributions Plan			$ 300,000
Non-Union Plans | Dogfish Head 401 (K) Plan | Company's match thereafter
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer match percentage			50.00%
Non-Union Plans | Dogfish Head 401 (K) Plan | Company's match for the first 3% of the eligible participants contribute
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer match percentage			100.00%
Contribution percentage by the company			3.00%
Union Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of retirement plans | CompensationPlan			2
Union Plans | Company Sponsored Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Eligibility timing			open to all union employees who are covered by the Company's collective bargaining agreement with Teamsters Local Union No. 1199 ("Local Union 1199"), or persons on leave from the Company who are employed by Local Union 1199, and in either case who have completed 12 consecutive months of employment with at least 750 hours worked
Pension contributions			$ 314,000	$ 315,000	$ 238,000
Eligibility period			12 months
Time required for eligibility			750 hours
Union Plans | Retiree Medical Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Eligibility period			20 years
Time required for eligibility			5 years
Benefit obligation, discount rate			3.32%	4.27%
Benefit obligation, rate of compensation increase			2.50%	2.50%	2.50%
Percentage paid for coverage			100.00%
Union Plans | Retiree Medical Plan | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Voluntarily retirement age			57 years
Union Plans | Retiree Medical Plan | Local #20 member
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Time required for eligibility			7 years
Retiree Medical Plan, last years of employment			10 years
Voluntarily retirement age			65 years
Union Plans | Retiree Medical Plan | Local #20 member | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Eligibility period			20 years
Union Plans | Samuel Adams Cincinnati Brewery 401 (k) Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Eligibility timing			all union employees upon commencement of employment or, if later, attaining age 21.
Voluntary contributions of annual compensation			60.00%