Stock-Based Employee Benefit Plans - Summary of Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Shares
Outstanding at September 30, 2023 (in shares)	227
Granted (in shares)	9
Exercised (in shares)	(47)
Outstanding at September 30, 2024 (in shares)	189	227
Options exercisable at September 30, 2024 (in shares)	119
Vested and expected to vest at September 30, 2024 (in shares)	185
Weighted- average Exercise Price
Outstanding at September 30, 2023 (in dollars per share)	$ 387.95
Granted (in dollars per share)	1,198
Exercised (in dollars per share)	176.46
Outstanding at September 30, 2024 (in dollars per share)	479.26	$ 387.95
Options exercisable at September 30, 2024 (in dollars per share)	290.75
Vested and expected to vest at September 30, 2024 (in dollars per share)	$ 471.93
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Additional Disclosures [Abstract]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	3 years 3 months 18 days
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term	1 year 11 months 23 days
Vested and expected to vest - Weighted average remaining term	3 years 3 months
Vested and expected to vest - Aggregate Intrinsic value	$ 272,681
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value	277,150
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value	$ 196,829
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of options granted (in dollars per share)	$ 419.00	$ 289.54	$ 134.91
Number of options that had exercise prices lower than the market price of common stock (in shares)	189
Market price of common stock (in dollars per share)	$ 1,943.52
Total intrinsic value of options exercised	$ 49,100	$ 16,700	$ 14,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	189	227
Equity Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average expected term (years)	4 years 5 months 15 days	5 years 2 months 23 days	4 years 5 months 4 days
Expected volatility (range), maximum	33.90%	35.50%	34.10%
Weighted average volatility	33.70%	33.50%	33.20%
Risk free interest rate, maximum	4.30%	4.49%	2.85%
Average expected dividend yield	0.00%	0.00%	0.00%
Expected volatility (range), minimum	33.60%	33.40%	32.90%
Risk free interest rate, minimum	4.18%	3.40%	1.18%