Acquisitions and Dispositions - Summary of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Business Acquisition [Line Items]
Goodwill	$ 336,602	$ 378,588	$ 168,491
Consideration transferred	42,000	490,600	122,100
Total Acquisitions
Business Acquisition [Line Items]
Accounts receivable	286	25,721	519
Inventories	6,424	61,754	19,044
Prepaid expenses	72	5,416	220
Property and equipment	11,588	38,256	42,503
Deposits		139
Operating lease right-of-use assets	3,820	27,195
Identifiable intangible assets	8,800	224,432	23,990
Goodwill	18,481	210,097	55,432
Accounts payable	(17)	(8,081)	(393)
Accrued expenses	(361)	(4,319)	(232)
Customer deposits	(1,013)	(14,448)	(5,281)
Notes payable – floor plan	(2,228)		(13,697)
Deferred tax liabilities		(20,892)
Long-term debt		(8,150)
Operating lease liabilities	(3,820)	(27,195)
Aggregate acquisition date fair value	42,032	509,925	122,105
Consideration transferred	$ 42,032	492,444	122,105
Cash acquired		(1,829)
Fair value of non-controlling interests		19,311
T-H Marine
Business Acquisition [Line Items]
Accounts receivable		8,955
Inventories		19,856
Prepaid expenses		1,547
Property and equipment		3,896
Deposits		0
Operating lease right-of-use assets		5,960
Identifiable intangible assets		105,500
Goodwill		51,694
Accounts payable		(3,876)
Accrued expenses		(1,697)
Customer deposits		(394)
Deferred tax liabilities		0
Long-term debt		0
Operating lease liabilities		(5,960)
Aggregate acquisition date fair value		185,481
Consideration transferred		185,481
Cash acquired		0
Fair value of non-controlling interests		0
Quality Boats
Business Acquisition [Line Items]
Accounts receivable		0
Inventories		5,937
Prepaid expenses		47
Property and equipment		803
Deposits		0
Operating lease right-of-use assets		11,877
Identifiable intangible assets		31,700
Goodwill		78,682
Accounts payable		0
Accrued expenses		0
Customer deposits		(5,047)
Deferred tax liabilities		0
Long-term debt		0
Operating lease liabilities		(11,877)
Aggregate acquisition date fair value		112,122
Consideration transferred		92,811
Cash acquired		0
Fair value of non-controlling interests		19,311
Denison Yachting
Business Acquisition [Line Items]
Accounts receivable		654
Inventories		1,981
Prepaid expenses		2,053
Property and equipment		293
Deposits		126
Operating lease right-of-use assets		1,221
Identifiable intangible assets		16,600
Goodwill		29,144
Accounts payable		(80)
Accrued expenses		(252)
Customer deposits		(5,524)
Deferred tax liabilities		0
Long-term debt		0
Operating lease liabilities		(1,221)
Aggregate acquisition date fair value		44,995
Consideration transferred		44,995
Cash acquired		0
Fair value of non-controlling interests		0
Ocean Bio-Chem
Business Acquisition [Line Items]
Accounts receivable		14,989
Inventories		24,362
Prepaid expenses		1,431
Property and equipment		32,037
Deposits		0
Operating lease right-of-use assets		762
Identifiable intangible assets		59,300
Goodwill		35,270
Accounts payable		(3,654)
Accrued expenses		(1,817)
Customer deposits		(176)
Deferred tax liabilities		(20,141)
Long-term debt		(8,150)
Operating lease liabilities		(762)
Aggregate acquisition date fair value		133,451
Consideration transferred		135,281
Cash acquired		(1,829)
Fair value of non-controlling interests		0
Walker Marine Group
Business Acquisition [Line Items]
Accounts receivable			129
Inventories			8,481
Prepaid expenses			39
Property and equipment			503
Identifiable intangible assets			8,520
Goodwill			26,927
Accounts payable			(213)
Accrued expenses			0
Customer deposits			(3,033)
Notes payable – floor plan			(7,563)
Aggregate acquisition date fair value			33,790
Consideration transferred			33,790
Roscioli Yachting Center
Business Acquisition [Line Items]
Accounts receivable			0
Inventories			87
Prepaid expenses			1
Property and equipment			41,300
Identifiable intangible assets			1,530
Goodwill			2,993
Accounts payable			(180)
Accrued expenses			(185)
Customer deposits			0
Notes payable – floor plan			0
Aggregate acquisition date fair value			45,546
Consideration transferred			45,546
Other Acquisitions
Business Acquisition [Line Items]
Accounts receivable		1,123	390
Inventories		9,618	10,476
Prepaid expenses		338	180
Property and equipment		1,227	700
Deposits		13
Operating lease right-of-use assets		7,375
Identifiable intangible assets		11,332	13,940
Goodwill		15,307	25,512
Accounts payable		(471)	0
Accrued expenses		(553)	(47)
Customer deposits		(3,307)	(2,248)
Notes payable – floor plan			(6,134)
Deferred tax liabilities		(751)
Long-term debt		0
Operating lease liabilities		(7,375)
Aggregate acquisition date fair value		33,876	42,769
Consideration transferred		33,876	$ 42,769
Cash acquired		0
Fair value of non-controlling interests		$ 0