Acquisitions (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2022 USD ($) Location	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($) Acquisition	Apr. 02, 2022 State Location	Dec. 31, 2021 Location	Dec. 01, 2021 Location	Oct. 02, 2021 Location	Aug. 01, 2021 Location	Dec. 31, 2020 Location	Dec. 01, 2020 Location
Acquisition [Abstract]
Number of acquisitions completed | Acquisition			0
Number of retail locations | Location	96
Cash paid for acquisition	$ 459,540	$ 107,467	$ 0
Note payable to seller	1,100	2,100
Payment of contingent consideration	15,300	9,200
Issuance of shares of Class A common stock	14,600	1,500
Minimum payout due of contingent consideration	5,900	200
Maximum payout due of contingent consideration	24,700
Summary of Assets Acquired and Liabilities Assumed [Abstract]
Goodwill	378,588	168,491	113,059
Consideration transferred	490,600	122,100
Revenue	1,744,822	1,228,206	1,022,970
Income before income tax expense	195,836	142,215	54,837
Costs related to acquisition	7,500
Accrued purchase consideration		1,900
Goodwill expected to be deductible for tax purposes	144,000	55,400
Unaudited Pro Forma Results of Operations [Abstract]
Pro forma revenues	1,885,896	1,755,678	1,514,417
Pro forma net income	$ 161,902	165,198	$ 80,866
Notes Payable [Member]
Acquisition [Abstract]
Interest rate	4.00%
Naples Boat Mart [Member]
Acquisition [Abstract]
Number of retail locations | Location							1
Norfolk Marine [Member]
Acquisition [Abstract]
Number of retail locations | Location						1
Quality Boats [Member]
Acquisition [Abstract]
Number of retail locations | Location					3
Percentage of economic interest retained by sellers	80.00%				20.00%
Percentage of remaining economic interest	20.00%				20.00%
Summary of Assets Acquired and Liabilities Assumed [Abstract]
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 [Member]
Acquisition [Abstract]
Number of retail locations | Location				20
Number of states | State				7
Summary of Assets Acquired and Liabilities Assumed [Abstract]
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
T-H Marine [Member]
Summary of Assets Acquired and Liabilities Assumed [Abstract]
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
Ocean Bio-Chem [Member]
Summary of Assets Acquired and Liabilities Assumed [Abstract]
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
Tom George Yacht Group [Member]
Acquisition [Abstract]
Number of retail locations | Location										2
Walker Marine Group [Member]
Acquisition [Abstract]
Number of retail locations | Location									5
Summary of Assets Acquired and Liabilities Assumed [Abstract]
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 [Member]
Acquisition [Abstract]
Number of retail locations | Location									1
Summary of Assets Acquired and Liabilities Assumed [Abstract]
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
Stone Harbor Marina [Member]
Acquisition [Abstract]
Number of retail locations | Location								1
Other Acquisitions [Member]
Summary of Assets Acquired and Liabilities Assumed [Abstract]
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
Total Acquisitions [Member]
Summary of Assets Acquired and Liabilities Assumed [Abstract]
Accounts receivable	25,721	519
Inventories	61,754	19,044
Prepaid expenses	5,416	220
Property and equipment	38,256	42,503
Deposits	139
Operating lease right-of-use assets	27,195
Identifiable intangible assets	224,432	23,990
Goodwill	210,097	55,432
Accounts payable	(8,081)	(393)
Accrued expenses	(4,319)	(232)
Customer deposits	(14,448)	(5,281)
Notes payable - floor plan		(13,697)
Deferred tax liabilities	(20,892)
Long-term debt	(8,150)
Operating lease liabilities	(27,195)
Aggregate acquisition date fair value	509,925	122,105
Consideration transferred	492,444	$ 122,105
Cash acquired	(1,829)
Fair value of non-controlling interests	19,311
Revenue	275,300
Income before income tax expense	$ 41,100