CONSOLIDATED STATEMENTS OF STOCKHOLDERS' AND MEMBERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Members Equity [Member]	Common Stock [Member] Class A Common Stock [Member]	Common Stock [Member] Class B Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Noncontrolling Interest [Member]	Total
Beginning balance at Sep. 30, 2018							$ 79,965
Increase (Decrease) in Temporary Equity [Roll Forward]
Net (loss) income							0
Distributions to members							(3,364)
Accumulated unpaid preferred returns							8,768
Accretion of redeemable preferred and issuance costs							649
Ending balance at Sep. 30, 2019							86,018
Beginning balance at Sep. 30, 2018	$ 15,963	$ 0	$ 0	$ 0	$ 0	$ 5,093	21,056
Beginning balance (in shares) at Sep. 30, 2018		0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	35,657	$ 0	$ 0	0	0	1,606	37,263
Distributions to members	(10,587)	0	0	0	0	(500)	(11,087)
Accumulated unpaid preferred returns	(8,768)	0	0	0	0	0	(8,768)
Accretion of redeemable preferred and issuance costs	(649)	0	0	0	0	0	(649)
Equity-based compensation	154	0	0	0	0	0	154
Ending balance at Sep. 30, 2019	31,770	$ 0	$ 0	0	0	6,199	37,969
Ending balance (in shares) at Sep. 30, 2019		0	0
Ending balance at Sep. 30, 2020							0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income							48,508
Ending balance at Sep. 30, 2020	0	$ 104	$ 46	105,947	16,757	50,433	173,287
Ending balance (in shares) at Sep. 30, 2020		10,392	4,583
Increase (Decrease) in Temporary Equity [Roll Forward]
Net (loss) income							0
Distributions to members							0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	0	$ 0	$ 0	0	79,059	37,354	116,413
Distributions to members	0	0	0	0	(1,160)	(8,813)	(9,973)
Dividends and distributions	0	0	0	0	(20,777)	(7,328)	(28,105)
Effect of September offering, including underwriter exercise of option to purchase shares	0	$ 4	$ (4)	4,146	0	(4,256)	(110)
Effect of September offering, including underwriter exercise of option to purchase shares (in shares)		387	(387)
Exchange of B shares for A shares	0	$ 24	$ (24)	38,485	0	(38,485)	0
Exchange of B shares for A shares (in shares)		2,377	(2,377)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	0	$ 0	$ 0	(4,186)	0	0	(4,186)
Shares issued upon vesting of equity-based awards, net of tax withholding	0	$ 1	$ 0	(803)	0	0	(802)
Shares issued upon vesting of equity-based awards, net of tax withholding (in shares)		85	0
Shares issued in connection with a business combination	0	$ 0	$ 0	1,495	0	0	1,495
Shares issued in connection with a business combination (in shares)		36	0
Adjustment to adopt Topic 842	0	$ 0	$ 0	0	1,073	0	1,073
Equity-based compensation	0	0	0	5,741	0	0	5,741
Ending balance at Sep. 30, 2021	$ 0	$ 133	$ 18	$ 150,825	$ 74,952	$ 28,905	$ 254,833
Ending balance (in shares) at Sep. 30, 2021		13,277	1,819