Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Current [Abstract]
Federal	$ 18,966	$ 4,384
State	3,108	1,436
Total current federal and state income tax expense	22,074	5,820
Deferred [Abstract]
Federal	3,341	395
State	387	114
Total deferred federal and state income tax expense	3,728	509
Income tax expense	$ 25,802	$ 6,329
Effective Income Tax Rate Reconciliation [Abstract]
Statutory federal tax rate	21.00%	21.00%	21.00%
Income attributable to non-controlling interests and nontaxable income	(5.50%)	(12.40%)	(21.00%)
State income taxes, net of federal benefit	2.40%	2.30%	0.00%
Other	0.80%	0.60%	0.00%
Effective income tax rate	18.70%	11.50%	0.00%
Deferred tax assets [Abstract]
Investment in partnerships	$ 19,293	$ 9,063
Tax receivable agreement	9,817	3,791
Total	29,110	12,854
Valuation allowance	0	0
Total deferred tax assets	29,110	12,854
Total deferred tax liabilities	0	0
Deferred tax assets, net	29,110	12,854
Tax receivable agreement liability	$ 40,100	$ 15,600
Percentage of net cash savings	85.00%