Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Employee benefits costs	$ 1.3	$ 0.9	$ 0.5
Employee Contributions up to 3%
Defined Benefit Plan Disclosure [Line Items]
Discretionary match percentage	100.00%
Percentage of compensation	3.00%
Employee Contributions Next 2%
Defined Benefit Plan Disclosure [Line Items]
Discretionary match percentage	50.00%
Percentage of compensation	2.00%