Stock-based Compensation Plans - Schedule of Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options Outstanding, Beginning balance	940,000	871,000	711,000
Number of Options, Granted	274,000	299,000	179,000
Number of Options, Exercised	(248,000)	(125,000)	(13,000)
Number of Options, Forfeited and expired	(44,000)	(105,000)	(6,000)
Number of Options Outstanding, Ending balance	922,000	940,000	871,000
Number of Options, vested and exercisable	402,000
Weighted Average Exercise Price, Beginning Balance	$ 35.18	$ 32.18	$ 26.28
Weighted Average Exercise Price, Granted	40.95	41.06	55.09
Weighted Average Exercise Price, Exercised	24.22	22.89	22.03
Weighted Average Exercise Price, Forfeited and expired	44.58	41.69	42.28
Weighted Average Exercise Price, Ending balance	39.39	$ 35.18	$ 32.18
Weighted Average Exercise Price, vested and exercisable	$ 36.07