Income Taxes - Current and Deferred Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Deferred Income Tax Assets And Liabilities
Income (loss) before income taxes	$ (23,090)	$ (15,201)	$ 143,496	$ 99,196
Current income tax expense (benefit)	(5,429)	(4,418)	30,958	31,382
Deferred income tax expense (benefit)	(1,032)	261	10,372	(2,495)
Total income tax expense (benefit)	$ (6,461)	$ (4,157)	$ 41,330	$ 28,887