Share-Based Compensation - Equity Incentive Plan Activity (Detail) - $ / shares shares in Thousands		12 Months Ended
		Sep. 30, 2025		Sep. 30, 2024	Sep. 30, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options, Total Options, Outstanding at September 30, 2024	[1]	1,384
Stock Options, Total Options, Granted		108
Stock Options, Total Options, Exercised / Vested		(171)
Stock Options, Total Options, Cancelled / Forfeited		(6)
Stock Options, Total Options, Outstanding at September 30, 2025	[1]	1,315	[2]	1,384
Stock Options, Total Options, Exercisable at September 30, 2025	[1],[2]	1,032
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2024		$ 56.65
Stock Options, Weighted Average Exercise Price, Granted		114.99
Stock Options, Weighted Average Exercise Price, Exercised / Vested		52.21
Stock Options, Weighted Average Exercise Price, Cancelled / Forfeited		74.21
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2025		61.96	[2]	$ 56.65
Stock Options, Weighted Average Exercise Price, Exercisable at September 30, 2025	[2]	$ 54.3
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock / Units, Outstanding at September 30, 2024	[3]	723
Restricted Stock / Units, Granted		166
Restricted Stock / Units, Performance-based adjustment	[4]	20
Restricted Stock / Units, Exercised / Vested		(292)
Restricted Stock / Units, Cancelled / Forfeited		(26)
Restricted Stock / Units, Outstanding at September 30, 2025	[3]	591	[2]	723
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2024		$ 70.25
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Granted		110.67		$ 75.98	$ 73.68
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Performance-based adjustment	[4]	78.68
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Exercised / Vested		59.95
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Cancelled / Forfeited		81.01
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2025		$ 86.48	[2]	$ 70.25

[1] Unvested stock options were approximately 283,000 and 373,000 at September 30, 2025 and 2024 and their weighted average grant date fair values were $89.84 and $70.24, respectively.

[2] Stock options outstanding include options vested and expected to vest in the future and have a weighted average remaining contractual life of 5.48 years.

[3] The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.

[4] Represents the net incremental number of shares issuable upon vesting of performance-based restricted stock units based on the Company’s actual financial performance metrics for fiscal 2025.