Goodwill and Intangible Assets - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Indefinite-Lived Intangible Assets [Line Items]
Impairment, intangible asset, indefinite-lived (excluding goodwill), extensible enumeration	Loss on impairment
Impairment, intangible asset, finite-lived (excluding goodwill), extensible enumeration	Loss on impairment
Loss on impairment	$ 147,402,000	$ 0	$ 0
Amortization expense	$ 13,436,000	7,630,000	0
Weighted average useful life	4 years 3 months 18 days
Goodwill	$ 336,602,000	378,588,000	$ 168,491,000
Domain Names
Indefinite-Lived Intangible Assets [Line Items]
Amortization expense	$ 528,000	104,000
Weighted average useful life	4 years 3 months 18 days
Internally Developed Software
Indefinite-Lived Intangible Assets [Line Items]
Amortization expense	$ 613,000	83,000
Weighted average useful life	4 years 4 months 24 days
Dealerships
Indefinite-Lived Intangible Assets [Line Items]
Loss on impairment	$ 6,500,000
Goodwill	295,300,000	280,000,000
Distribution
Indefinite-Lived Intangible Assets [Line Items]
Loss on impairment	140,900,000
Goodwill	$ 41,300,000	$ 98,600,000