Income Taxes - Current and Deferred Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Deferred Income Tax Assets And Liabilities
Income before income taxes	$ 52,688	$ 39,537
Current income tax expense	11,227	10,446
Deferred income tax expense	3,601	1,336
Total income tax expense	$ 14,828	$ 11,782