Stock-Based Employee Benefit Plans - Summary of Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares
Shares
Outstanding at September 30, 2019 (in shares) | shares	246
Granted (in shares) | shares	21
Exercised (in shares) | shares	(40)
Forfeited (in shares) | shares	(1)
Outstanding at September 30, 2020 (in shares) | shares	226
Options exercisable at September 30, 2020 (in shares) | shares	163
Vested and expected to vest at September 30, 2020 (in shares) | shares	225
Weighted- average Exercise Price
Outstanding at September 30, 2019 (in dollars per share) | $ / shares	$ 166.80
Granted (in dollars per share) | $ / shares	485.77
Exercised (in dollars per share) | $ / shares	108.81
Forfeited (in dollars per share) | $ / shares	506.91
Outstanding at September 30, 2020 (in dollars per share) | $ / shares	205.90
Options exercisable at September 30, 2020 (in dollars per share) | $ / shares	168.38
Vested and expected to vest at September 30, 2020 (in dollars per share) | $ / shares	$ 204.66
Weighted- average Remaining Contractual Term
Outstanding at September 30, 2021	3 years 5 months 8 days
Exercisable at September 30, 2021	2 years 10 months 6 days
Vested and expected to vest at September 30, 2018	3 years 5 months 1 day
Aggregate Intrinsic Value
Outstanding at September 30, 2021 | $	$ 45,263,900
Exercisable at September 30, 2021 | $	37,659,408
Vested and expected to vest at September 30, 2017 | $	$ 45,173,168