Segment Information - Reportable Segment Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Total revenues	$ 1,872,334	$ 1,772,630	$ 1,936,310
Total cost of sales	1,445,312	1,337,567	1,401,184
Selling, general and administrative expenses	343,285	332,680	345,524
Interest expense – floor plan	28,469	34,087	25,080
Segment income	(116,230)	(6,176)	(39,111)
Dealerships
Segment Reporting Information [Line Items]
Total revenues	1,724,981	1,616,570	1,755,227
Total cost of sales	1,344,696	1,233,143	1,279,673
Selling, general and administrative expenses	283,215	276,113	286,426
Interest expense – floor plan	28,469	34,087	25,080
Segment income	68,601	73,227	164,048
Distribution
Segment Reporting Information [Line Items]
Selling, general and administrative expenses	49,571	48,124	50,137
Segment income	1,511	9,230	12,325
New boat
Segment Reporting Information [Line Items]
Total revenues	1,158,165	1,118,292	1,223,691
Total cost of sales	974,951	921,406	955,222
New boat | Dealerships
Segment Reporting Information [Line Items]
Total revenues	1,158,165	1,118,292	1,223,691
Total cost of sales	973,411	919,596	955,222
Pre-owned boat
Segment Reporting Information [Line Items]
Total revenues	363,906	312,193	334,477
Total cost of sales	298,361	248,068	258,524
Pre-owned boat | Dealerships
Segment Reporting Information [Line Items]
Total revenues	363,906	312,193	334,477
Total cost of sales	298,361	248,068	258,524
Finance & insurance income
Segment Reporting Information [Line Items]
Total revenues	54,959	51,494	56,325
Finance & insurance income | Dealerships
Segment Reporting Information [Line Items]
Total revenues	54,959	51,494	56,325
Service, parts & other
Segment Reporting Information [Line Items]
Total revenues	295,304	290,651	321,817
Total cost of sales	172,000	168,093	187,438
Service, parts & other | Dealerships
Segment Reporting Information [Line Items]
Total revenues	147,951	134,591	140,734
Total cost of sales	72,924	65,479	65,927
Service, parts & other | Distribution
Segment Reporting Information [Line Items]
Total revenues	147,353	156,060	181,083
Total cost of sales	$ 96,271	$ 98,706	$ 118,621