Income Taxes - Summary of Reconciliation of Changes in Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, beginning balance	$ 2,871	$ 2,323	$ 1,559
Increases in tax positions for prior years	15	58	278
Decreases in tax positions for prior years	(8)	(1)	(2)
Increases in tax positions for current year	458	664	735
Lapse of the statute of limitations	(449)	(173)	(247)
Unrecognized tax benefits, ending balance	$ 2,887	$ 2,871	$ 2,323