Subsequent Event - Additional Information (Detail) - USD ($) $ in Millions	Oct. 05, 2017	Sep. 30, 2017
Schedule Of Common Share Purchase [Line Items]
Increase of expenditure limit for Company's Stock Repurchase Program	$ 150.0
Stock Repurchase Program limit	$ 931.0	$ 781.0

Stock Repurchase Program, Additional Authorized Amount

No definition available.

Name:	sam_StockRepurchaseProgramAdditionalAuthorizedAmount
Namespace Prefix:	sam_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration