Stock-Based Compensation - Equity Incentive Plan Activity (Detail) - $ / shares shares in Thousands		12 Months Ended
		Sep. 30, 2023		Sep. 30, 2022	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options, Total Options, Outstanding at September 30, 2022	[1]	1,574
Stock Options, Total Options, Granted	[1]	157
Stock Options, Total Options, Exercised / Vested	[1]	(75)
Stock Options, Total Options, Cancelled / Forfeited	[1]	(15)
Stock Options, Total Options, Outstanding at September 30, 2023	[1]	1,641	[2]	1,574
Stock Options, Total Options, Exercisable at September 30, 2023	[1]	1,172
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2022		$ 49.89
Stock Options, Weighted Average Exercise Price, Granted		73.84
Stock Options, Weighted Average Exercise Price, Exercised / Vested		47.77
Stock Options, Weighted Average Exercise Price, Cancelled / Forfeited		49.88
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2023		52.27	[2]	$ 49.89
Stock Options, Weighted Average Exercise Price, Exercisable at September 30, 2023		$ 50.02
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock / Units, Outstanding at September 30, 2022	[3]	1,012
Restricted Stock / Units, Granted	[3]	225
Restricted Stock / Units, Performance-based adjustment	[3],[4]	20
Restricted Stock / Units, Exercised / Vested	[3]	(275)
Restricted Stock / Units, Cancelled / Forfeited	[3]	(44)
Restricted Stock / Units, Outstanding at September 30, 2023	[3]	938	[2]	1,012
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2022		$ 48.95
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Granted		73.68		$ 58.72	$ 41.92
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Performance-based adjustment	[4]	51.88
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Exercised / Vested		50.43
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Cancelled / Forfeited		50.2
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2023		$ 54.45	[2]	$ 48.95

[1] Unvested stock options were approximately 469,000 and 651,000 at September 30, 2023 and 2022 and their weighted average grant date fair values were $57.92 and $49.30, respectively.

[2] Stock options outstanding include options vested and expected to vest in the future and have a weighted average remaining contractual life of 6.13 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 2023.