Summary of Significant Accounting Policies - Software Development and Cloud Computing Arrangement Implementation Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Finite-Lived Intangible Assets [Line Items]
Intangible asset estimated useful lives (in years)	10 years
Intangible asset non-current	$ 205,391	$ 212,324	$ 306,471
Selling, general and administrative expenses	$ 332,680	345,524	$ 302,113
Domain Names & Internally Developed Software | Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible asset estimated useful lives (in years)	3 years
Domain Names & Internally Developed Software | Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible asset estimated useful lives (in years)	5 years
Cloud Computing Arrangements
Finite-Lived Intangible Assets [Line Items]
Expected amortization recognition period	1 year
Selling, general and administrative expenses	$ 300	100
Intangible Assets, Gross (Excluding Goodwill)	1,700	5,400
Finite-Lived Intangible Assets, Accumulated Amortization	$ 400	$ 100