Segment Information - Reportable Segment Financial Information (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)	Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Mar. 31, 2026 USD ($) segment	Mar. 31, 2025 USD ($)
Segment Reporting Information [Line Items]
Total revenues	$ 442,293		$ 483,521		$ 822,854	$ 859,335
Total cost of sales	336,763		373,110		627,931	664,870
Selling, general and administrative expenses	85,661		87,791		167,011	166,851
Interest expense – floor plan	6,611		7,504		13,767	14,530
Net loss	(12,901)	$ (7,711)	(375)	$ (13,612)	$ (20,612)	(13,987)
Number of reportable segments | segment					2
Interest expense – other	(7,345)		(9,100)		$ (15,981)	(18,088)
Restructuring and impairment	(6,594)		(388)		(14,026)	(2,286)
Change in fair value of contingent consideration	0		(66)		(203)	(308)
Equity-based compensation	(2,805)		(2,088)		(4,941)	(4,258)
Transaction costs	(1,464)		(377)		(2,636)	(936)
Depreciation and amortization	(4,453)		(6,171)		(9,443)	(12,208)
Other expense, net	(1,056)		(190)		(1,181)	(1,077)
Net loss before income tax benefit	(7,375)		(523)		(28,466)	(19,397)
Operating Segments
Segment Reporting Information [Line Items]
Net loss	16,342		17,857		19,945	19,764
Dealerships
Segment Reporting Information [Line Items]
Total revenues	411,835		446,290		759,689	793,915
Total cost of sales	315,719		348,441		583,521	619,661
Selling, general and administrative expenses	74,328		73,941		142,560	139,754
Interest expense – floor plan	6,611		7,504		13,767	14,530
Net loss	15,177		16,404		19,841	19,970
Interest expense – other	(7,345)		(9,100)		(15,981)	(18,088)
Dealerships | Operating Segments
Segment Reporting Information [Line Items]
Net loss	15,177		16,404		19,841	19,970
Distribution
Segment Reporting Information [Line Items]
Selling, general and administrative expenses	8,528		11,762		19,510	22,839
Net loss	1,165		1,453		104	(206)
Interest expense – other	0		0		0	0
Distribution | Operating Segments
Segment Reporting Information [Line Items]
Net loss	1,165		1,453		104	(206)
New boat
Segment Reporting Information [Line Items]
Total revenues	272,042		309,500		505,307	557,497
Total cost of sales	223,583		259,217		418,540	470,338
New boat | Dealerships
Segment Reporting Information [Line Items]
Total revenues	272,042		309,500		505,307	557,497
Total cost of sales	223,583		259,217		418,540	469,291
Pre-owned boat
Segment Reporting Information [Line Items]
Total revenues	94,367		89,728		164,782	146,526
Total cost of sales	76,650		73,877		132,463	119,459
Pre-owned boat | Dealerships
Segment Reporting Information [Line Items]
Total revenues	94,367		89,728		164,782	146,526
Total cost of sales	76,650		73,877		132,463	119,459
Finance & insurance income
Segment Reporting Information [Line Items]
Total revenues	14,021		15,003		22,913	24,403
Finance & insurance income | Dealerships
Segment Reporting Information [Line Items]
Total revenues	14,021		15,003		22,913	24,403
Service, parts & other
Segment Reporting Information [Line Items]
Total revenues	61,863		69,290		129,852	130,909
Total cost of sales	36,530		40,016		76,928	75,073
Service, parts & other | Dealerships
Segment Reporting Information [Line Items]
Total revenues	31,405		32,059		66,687	65,489
Total cost of sales	15,486		15,347		32,518	30,911
Service, parts & other | Distribution
Segment Reporting Information [Line Items]
Total revenues	30,458		37,231		63,165	65,420
Total cost of sales	$ 20,765		$ 24,016		$ 43,551	$ 42,787