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, 2021	Dec. 31, 2020
Numerator for diluted and basic earnings per share:
Net income	$ 84,959	$ 86,492
Denominator - share:
Basic weighted-average shares (in shares)	27,167	29,127
Effect of dilutive securities (in shares)	357	662
Diluted weighted-average shares (in shares)	27,524	29,789
Earnings per share:
Basic (in dollars per share)	$ 3.13	$ 2.97
Diluted (in dollars per share)	$ 3.09	$ 2.90