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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Numerator for diluted and basic earnings per share:
Net income	$ 93,500	$ 151,198	$ 282,842	$ 306,364
Denominator — share:
Basic weighted-average shares (in shares)	25,634	28,687	26,319	28,967
Effect of dilutive securities (in shares)	233	508	289	538
Diluted weighted-average shares (in shares)	25,867	29,195	26,608	29,505
Earnings per share:
Basic (in dollars per share)	$ 3.65	$ 5.27	$ 10.75	$ 10.58
Diluted (in dollars per share)	$ 3.61	$ 5.18	$ 10.63	$ 10.38