Equity-Based Compensation (Details) - USD ($)		12 Months Ended
	Jun. 25, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense		$ 10,452,000	$ 6,124,000	$ 1,567,000
Income tax benefits related to equity-based compensation		604,000	160,000	0
TRA non-participation compensatory shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense	$ 741,000	0	0	741,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation expense		$ 10,452,000	$ 6,124,000	$ 826,000