CONDENSED 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, 2019							$ 86,018
Increase (Decrease) in Temporary Equity [Roll Forward]
Distributions to members							(1,310)
Accumulated unpaid preferred returns							2,183
Accretion of redeemable preferred and issuance costs							162
Ending balance at Dec. 31, 2019							87,053
Beginning balance at Sep. 30, 2019	$ 31,770	$ 0	$ 0	$ 0	$ 0	$ 6,199	37,969
Beginning balance (in shares) at Sep. 30, 2019		0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(1,314)	$ 0	$ 0	0	0	247	(1,067)
Distributions to members	(189)	0	0	0	0	(732)	(921)
Accumulated unpaid preferred returns	(2,183)	0	0	0	0	0	(2,183)
Accretion of redeemable preferred and issuance costs	(162)	0	0	0	0	0	(162)
Equity-based compensation	39	0	0	0	0	0	39
Ending balance at Dec. 31, 2019	27,961	$ 0	$ 0	0	0	5,714	33,675
Ending balance (in shares) at Dec. 31, 2019		0	0
Beginning balance at Sep. 30, 2020							0
Increase (Decrease) in Temporary Equity [Roll Forward]
Distributions to members							0
Ending balance at Dec. 31, 2020							0
Beginning balance at Sep. 30, 2020	0	$ 104	$ 46	105,947	16,757	50,433	173,287
Beginning balance (in shares) at Sep. 30, 2020		10,392	4,583
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	0	$ 0	$ 0	0	7,788	3,987	11,775
Distributions to members	0	0	0	0	0	(1,319)	(1,319)
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	$ 1	$ (1)	916	0	(916)	0
Exchange of B shares for A shares (in shares)		88	(88)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	0	$ 0	$ 0	(228)	0	0	(228)
Equity-based compensation	0	0	0	1,078	0	0	1,078
Ending balance at Dec. 31, 2020	$ 0	$ 109	$ 41	$ 111,859	$ 24,545	$ 47,929	$ 184,483
Ending balance (in shares) at Dec. 31, 2020		10,867	4,108