Income Taxes - Current and Deferred Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Deferred Income Tax Assets And Liabilities
Income before income taxes	$ 96,244	$ 86,294	$ 114,397	$ 105,296
Current income tax expense	29,035	35,408	35,800	42,095
Deferred income tax benefit	(1,165)	(11,155)	(2,756)	(12,379)
Total income tax expense	$ 27,870	$ 24,253	$ 33,044	$ 29,716