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
	Dec. 31, 2024	Dec. 31, 2023
Numerator for diluted and basic earnings per share:
Net income	$ 152,528	$ 121,065
Denominator — share:
Basic weighted-average shares (in shares)	24,378	24,764
Effect of dilutive securities (in shares)	449	455
Diluted weighted-average shares (in shares)	24,827	25,219
Earnings per share:
Basic (in dollars per share)	$ 6.26	$ 4.89
Diluted (in dollars per share)	$ 6.14	$ 4.80