Earnings per Share - Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Numerator for diluted and basic earnings per share:
Net income	$ 126,256	$ 128,758	$ 377,120	$ 327,951
Denominator — share:
Basic weighted-average shares (in shares)	24,646	24,959	24,743	25,040
Effect of dilutive securities (in shares)	369	378	386	359
Diluted weighted-average shares (in shares)	25,015	25,337	25,129	25,399
Earnings per share:
Basic (in dollars per share)	$ 5.12	$ 5.16	$ 15.24	$ 13.10
Diluted (in dollars per share)	$ 5.05	$ 5.08	$ 15.01	$ 12.91