Restructuring and Impairment (Details) - USD ($)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges	$ 15,318,000	$ 147,402,000
2023 Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges	0	147,400,000	$ 0
2023 Impairment | Dealerships
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges		6,500,000
2023 Impairment | Distribution
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges		140,900,000
2024 Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges	15,300,000	0	$ 0
2024 Restructuring | Dealerships
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges	13,000,000
2024 Restructuring | Distribution
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges	2,300,000
2024 Restructuring | Restructuring and impairment
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges	12,400,000
2024 Restructuring | New boat cost of sales
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges	1,800,000
2024 Restructuring | Service, Parts and Other Cost of Sales
Restructuring Cost and Reserve [Line Items]
Restructuring Costs and Asset Impairment Charges	1,100,000
Other Accounts Payable and Accrued Liabilities | 2024 Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 1,000,000.0	$ 0