Acquisitions and Dispositions - Narrative (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2023 USD ($) renewal_option property location	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 01, 2023 location	Apr. 01, 2022 state location	Dec. 31, 2021 location	Dec. 01, 2021 location	Oct. 01, 2021 location	Aug. 01, 2021 location	Dec. 31, 2020 location	Dec. 01, 2020 location
Business Acquisition [Line Items]
Number of retail locations | location	98
Consideration transferred	$ 42,000	$ 490,600	$ 122,100
Cash paid for acquisition	28,882	459,540	107,467
Noncash acquisition purchase price funded by affiliate financing	10,600	0	0
Contingent consideration, liability	2,600	15,300	9,200
Revenue from contract with customer	1,936,310	1,744,822	1,228,206
Net (loss) income before income tax expense	(42,523)	195,836	142,215
Costs related to acquisition	1,200
Business combination, consideration transferred, liabilities incurred		1,100	2,100
Issuance of shares of Class A common stock		14,600	1,900
Minimum payout due of contingent consideration		5,900	200
Maximum payout due of contingent consideration		24,700
Goodwill expected to be deductible for tax purposes	$ 15,900	$ 173,200	55,400
Class A Common Stock
Business Acquisition [Line Items]
Issuance of shares of Class A common stock			1,500
Notes Payable
Business Acquisition [Line Items]
Debt instrument, interest rate, stated percentage		4.00%
Harbor Pointe Marina
Business Acquisition [Line Items]
Number of retail locations | location				1
Harbor View Marine
Business Acquisition [Line Items]
Number of retail locations | property	2
Gain (loss) on sale and leaseback transaction	$ 0
Term of contract	15 years
Number of lease renewal options | renewal_option	2
Renewal term	5 years
Total Acquisitions
Business Acquisition [Line Items]
Consideration transferred	$ 42,032	$ 492,444	122,105
Revenue from contract with customer	60,900
Net (loss) income before income tax expense	$ 6,300
Naples Boat Mart
Business Acquisition [Line Items]
Number of retail locations | location								1
Norfolk Marine
Business Acquisition [Line Items]
Number of retail locations | location							1
Quality Boats
Business Acquisition [Line Items]
Number of retail locations | location						3
Consideration transferred		92,811
Percentage of economic interest retained by sellers	80.00%					20.00%
Denison Yachting
Business Acquisition [Line Items]
Consideration transferred		$ 44,995
Number of retail locations | location					20
Number of states | state					7
Tom George Yacht Group
Business Acquisition [Line Items]
Number of retail locations | location											2
Walker Marine Group
Business Acquisition [Line Items]
Number of retail locations | location										5
Consideration transferred			33,790
Roscioli Yachting Center
Business Acquisition [Line Items]
Number of retail locations | location										1
Consideration transferred			$ 45,546
Stone Harbor Marina
Business Acquisition [Line Items]
Number of retail locations | location									1