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Company Background and Basis of Presentation - Additional Information (Detail)
12 Months Ended
Sep. 30, 2020
Store
State
Sep. 30, 2019
Sep. 30, 2018
Concentration Risk [Line Items]      
Number of retail locations | Store 57    
Number of states wherein retail locations are established | State 16    
Product Concentration Risk [Member] | Sales [Member]      
Concentration Risk [Line Items]      
Revenue percentage from sale of boats 100.00% 100.00% 100.00%
Product Concentration Risk [Member] | Brunswick [Member] | Sales [Member]      
Concentration Risk [Line Items]      
Revenue percentage from sale of boats 33.00%    
Product Concentration Risk [Member] | Brunswick Sea Ray Boat [Member] | Brunswick [Member] | Sales [Member]      
Concentration Risk [Line Items]      
Revenue percentage from sale of boats 15.00%    
Product Concentration Risk [Member] | Brunswick Boston Whaler Boats [Member] | Brunswick [Member] | Sales [Member]      
Concentration Risk [Line Items]      
Revenue percentage from sale of boats 16.00%    
Product Concentration Risk [Member] | Azimut Benetti Groups and Yachts | Sales [Member]      
Concentration Risk [Line Items]      
Revenue percentage from sale of boats 9.00%    
Geographic Concentration Risk [Member] | Sales [Member] | Florida [Member]      
Concentration Risk [Line Items]      
Revenue percentage from sale of boats 54.00% 54.00% 51.00%