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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Numerator for diluted and basic earnings per share:
Net income	$ 128,758	$ 93,500	$ 327,951	$ 282,842
Denominator — share:
Basic weighted-average shares (in shares)	24,959	25,634	25,040	26,319
Effect of dilutive securities (in shares)	378	233	359	289
Diluted weighted-average shares (in shares)	25,337	25,867	25,399	26,608
Earnings per share:
Basic (in dollars per share)	$ 5.16	$ 3.65	$ 13.10	$ 10.75
Diluted (in dollars per share)	$ 5.08	$ 3.61	$ 12.91	$ 10.63