Income Taxes - Current and Deferred Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Deferred Income Tax Assets And Liabilities
Income before income taxes	$ 120,678	$ 96,244	$ 166,586	$ 114,397
Current income tax expense	26,030	29,035	36,387	35,800
Deferred income tax expense (benefit)	8,737	(1,165)	11,404	(2,756)
Total income tax expense	$ 34,767	$ 27,870	$ 47,791	$ 33,044