Segment Information - Reportable Segment Financial Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($) segment	Jun. 30, 2025 USD ($)
Segment Reporting [Line Items]
Total revenues	$ 530,711	$ 552,864	$ 1,353,565	$ 1,412,199
Total cost of sales	403,230	424,201	1,031,161	1,089,071
Selling, general and administrative expenses	87,243	92,138	254,254	258,989
Interest expense – floor plan	6,763	7,340	$ 20,530	21,870
Number of reportable segments | segment			2
Interest expense – other	(7,070)	(9,041)	$ (23,051)	(27,129)
Restructuring and impairment	(304)	(727)	(14,330)	(3,013)
Change in fair value of contingent consideration	0	(144)	(203)	(452)
Equity-based compensation	(4,006)	(2,459)	(8,947)	(6,717)
Transaction costs	(210)	(175)	(2,846)	(1,111)
Depreciation and amortization	(4,352)	(6,301)	(13,795)	(18,509)
Other expense, net	150	224	(1,031)	(853)
Income tax expense	10,293	3,507	2,439	(1,903)
Net loss before income tax benefit	21,966	14,222	(6,500)	(5,175)
Operating Segments
Segment Reporting [Line Items]
Segment income	37,758	32,845	57,703	52,609
Dealership
Segment Reporting [Line Items]
Total revenues	501,372	512,761	1,261,061	1,306,676
Total cost of sales	382,998	398,331	966,519	1,017,992
Selling, general and administrative expenses	75,427	76,454	217,988	216,208
Segment income	36,184	30,636	56,024	50,606
Interest expense – floor plan	6,763	7,340	20,530	21,870
Interest expense – other	(7,070)	(9,041)	(23,051)	(27,129)
Net loss before income tax benefit	36,184	30,636
Distribution
Segment Reporting [Line Items]
Selling, general and administrative expenses	7,810	13,225	27,319	36,064
Segment income	1,574	2,209	1,679	2,003
Interest expense – other	0	0	0	0
New boat
Segment Reporting [Line Items]
Total revenues	319,960	326,134	825,267	883,631
Total cost of sales	262,826	274,184	681,366	744,522
New boat | Dealership
Segment Reporting [Line Items]
Total revenues	319,960	326,134	825,267	883,631
Total cost of sales	262,826	273,691	681,366	742,982
Pre-owned boat
Segment Reporting [Line Items]
Total revenues	121,058	125,941	285,840	272,467
Total cost of sales	96,559	103,406	229,022	222,865
Pre-owned boat | Dealership
Segment Reporting [Line Items]
Total revenues	121,058	125,941	285,840	272,467
Total cost of sales	96,559	103,406	229,022	222,865
Finance & insurance income
Segment Reporting [Line Items]
Total revenues	17,293	17,782	40,206	42,185
Finance & insurance income | Dealership
Segment Reporting [Line Items]
Total revenues	17,293	17,782	40,206	42,185
Service, parts & other
Segment Reporting [Line Items]
Total revenues	72,400	83,007	202,252	213,916
Total cost of sales	43,845	46,611	120,773	121,684
Service, parts & other | Dealership
Segment Reporting [Line Items]
Total revenues	43,061	42,904	109,748	108,393
Total cost of sales	23,613	21,234	56,131	52,145
Service, parts & other | Distribution
Segment Reporting [Line Items]
Total revenues	29,339	40,103	92,504	105,523
Total cost of sales	$ 19,955	$ 24,669	$ 63,506	$ 67,456