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Company Background - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2018 Store State
Concentration Risk [Line Items]
Number of retail locations | Store				63
Number of states wherein retail locations are established | State				16
Product Concentration Risk [Member] | Brunswick [Member] | Sales [Member]
Concentration Risk [Line Items]
Revenue percentage from sale of boats	42.00%
Product Concentration Risk [Member] | Brunswick Sea Ray Boat [Member] | Brunswick [Member] | Sales [Member]
Concentration Risk [Line Items]
Revenue percentage from sale of boats	23.00%
Product Concentration Risk [Member] | Brunswick Boston Whaler Boats [Member] | Brunswick [Member] | Sales [Member]
Concentration Risk [Line Items]
Revenue percentage from sale of boats	17.00%
Product Concentration Risk [Member] | Azimut Benetti Groups | Sales [Member]
Concentration Risk [Line Items]
Revenue percentage from sale of boats	9.00%
Supplier Concentration Risk [Member] | Brunswick [Member] | Sales [Member]
Concentration Risk [Line Items]
Revenue percentage from sale of boats	55.00%
Geographic Concentration Risk [Member] | Sales [Member] | Florida [Member]
Concentration Risk [Line Items]
Revenue percentage from sale of boats	55.00%	55.00%	53.00%

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-Name Accounting Standards Codification
-Topic 275
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