Inventories - Summary of Inventories (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Inventory [Line Items]
Inventories, net	$ 477,468	$ 377,074
New Boats, Motors, and Trailers [Member]
Inventory [Line Items]
Inventories, net	413,335	332,320
Used Boats, Motors, and Trailers [Member]
Inventory [Line Items]
Inventories, net	56,363	35,999
Parts, Accessories, and Other [Member]
Inventory [Line Items]
Inventories, net	$ 7,770	$ 8,755

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118951113&loc=d3e6676-107765

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116846819&loc=d3e3927-108312

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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