Equity Incentive Plans - Additional Information (Details)		12 Months Ended
		Sep. 30, 2025 USD ($) shares $ / shares	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock Issuable per Restricted Stock Unit | shares		1
Stock-based compensation		$ 216,205,000	$ 223,461,000	$ 206,459,000
Total unrecognized compensation cost		$ 201,500,000
Weighted average remaining recognition period, in months		18 months
Common stock were available for grant under the 2000 plan | shares		4,900,000
Common stock were reserved for issuance | shares		1,900,000
ESPP maximum contribution percentage		10.00%
ESPP maximum contribution amount by employee		$ 25,000
ESPP purchase price as a % of stock price		85.00%
Vesting term for outstanding awards		1 year 1 month 6 days
Shares withheld for tax withholding obligation | shares		400,000	600,000	600,000
Payments of withholding taxes in connection with vesting of stock-based awards		$ 80,205,000	$ 102,001,000	$ 82,448,000
Liability classified awards related to stock-based compensation		51,300,000	47,700,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation		$ 7,100,000	$ 6,800,000	$ 6,800,000
Restricted Shares and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share | $ / shares		$ 186.37	$ 164.73	$ 130.64
TSR Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share | $ / shares		243.47
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share | $ / shares	[1]	$ 186.37
Payments of withholding taxes in connection with vesting of stock-based awards		$ 80,400,000	$ 101,900,000	$ 82,800,000

[1] RSUs granted include 17 shares from prior period rTSR awards that were earned upon achievement of the performance criteria and vested in November 2024 and 10 shares from prior period performance-based awards that were earned upon achievement of the performance criteria and vested in November 2024.