Acquisitions and Dispositions - Summary of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	May 01, 2024	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Business Acquisition [Line Items]
Goodwill		$ 336,602	$ 336,602	$ 378,588
Consideration transferred			42,000	490,600
Total Acquisitions
Business Acquisition [Line Items]
Accounts receivable			286	25,721
Inventories			6,424	61,754
Prepaid expenses			72	5,416
Property and equipment			11,588	38,256
Deposits				139
Operating lease right-of-use assets			3,820	27,195
Identifiable intangible assets			8,800	224,432
Goodwill			18,481	210,097
Accounts payable			(17)	(8,081)
Accrued expenses			(361)	(4,319)
Customer deposits			(1,013)	(14,448)
Notes payable - floor plan			(2,228)
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
Consideration transferred			$ 42,032	492,444
Cash acquired				(1,829)
Fair value of non-controlling interests				19,311
Garden State Yacht Sales
Business Acquisition [Line Items]
Accounts receivable	$ 113
Inventories	6,676
Prepaid expenses	11
Property and equipment	478
Operating lease right-of-use assets	4,360
Accounts payable	(1,263)
Accrued expenses	(36)
Customer deposits	(267)
Operating lease liabilities	(4,360)
Aggregate acquisition date fair value	5,712
Business Combination, Consideration Transferred	$ 5,712
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
Other Acquisitions
Business Acquisition [Line Items]
Accounts receivable				1,123
Inventories				9,618
Prepaid expenses				338
Property and equipment				1,227
Deposits				13
Operating lease right-of-use assets				7,375
Identifiable intangible assets				11,332
Goodwill				15,307
Accounts payable				(471)
Accrued expenses				(553)
Customer deposits				(3,307)
Deferred tax liabilities				(751)
Long-term debt				0
Operating lease liabilities				(7,375)
Aggregate acquisition date fair value				33,876
Consideration transferred				33,876
Cash acquired				0
Fair value of non-controlling interests				$ 0