Income Taxes - Current and Deferred Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Deferred Income Tax Assets And Liabilities
Income before income taxes	$ 114,279	$ 117,316	$ 134,606	$ 170,004
Current income tax expense	27,671	23,130	34,193	34,357
Deferred income tax expense	5,229	9,022	4,545	12,623
Total income tax expense	$ 32,900	$ 32,152	$ 38,738	$ 46,980