Income Taxes - Current and Deferred Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Deferred Income Tax Assets And Liabilities
Income (loss) before income taxes	$ (15,963)	$ (2,051)	$ 154,041	$ 120,594
Current income tax expense (benefit)	(3,968)	(629)	30,389	35,631
Deferred income tax expense (benefit)	59	(1,376)	12,682	(1,154)
Total income tax expense (benefit)	$ (3,909)	$ (2,005)	$ 43,071	$ 34,477