CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member] Class A Common Stock [Member]	Common Stock [Member] Class B Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Non-controlling Interest [Member]	Total
Beginning balance at Sep. 30, 2020	$ 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 income	$ 0	$ 0	0	7,788	3,987	11,775
Distributions to members	0	0	0	0	(1,319)	(1,319)
Effect of September offering, including underwriter exercise of option to purchase shares	$ 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	$ 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	(228)	0	0	(228)
Adjustment to adopt Topic 842	0	0	0	1,073	0	1,073
Equity-based compensation	0	0	1,078	0	0	1,078
Ending balance at Dec. 31, 2020	$ 109	$ 41	111,859	25,618	47,929	185,556
Ending balance (in shares) at Dec. 31, 2020	10,867	4,108
Beginning balance at Sep. 30, 2020	$ 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 income						42,367
Ending balance at Mar. 31, 2021	$ 110	$ 41	113,088	46,032	57,348	216,619
Ending balance (in shares) at Mar. 31, 2021	10,968	4,071
Beginning balance at Dec. 31, 2020	$ 109	$ 41	111,859	25,618	47,929	185,556
Beginning balance (in shares) at Dec. 31, 2020	10,867	4,108
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	$ 0	0	20,475	10,117	30,592
Distributions to members	0	0	0	(61)	(140)	(201)
Exchange of B shares for A shares	$ 0	$ 0	558	0	(558)	0
Exchange of B shares for A shares (in shares)	37	(37)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	$ 0	$ 0	(6)	0	0	(6)
Shares issued upon vesting of equity-based awards, net of tax withholding	$ 1	$ 0	(450)	0	0	(449)
Shares issued upon vesting of equity-based awards, net of tax withholding (in shares)	64	0
Equity-based compensation	$ 0	$ 0	1,127	0	0	1,127
Ending balance at Mar. 31, 2021	$ 110	$ 41	113,088	46,032	57,348	216,619
Ending balance (in shares) at Mar. 31, 2021	10,968	4,071
Beginning balance at Sep. 30, 2021	$ 133	$ 18	150,825	74,952	28,905	254,833
Beginning balance (in shares) at Sep. 30, 2021	13,277	1,819
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	$ 0	0	20,019	3,467	23,486
Distributions to members	0	0	0	(442)	(177)	(619)
Non-controlling interest in subsidiary	0	0	0	0	19,311	19,311
Exchange of B shares for A shares	$ 4	$ (4)	7,405	0	(7,405)	0
Exchange of B shares for A shares (in shares)	389	(389)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	$ 0	$ 0	(283)	0	0	(283)
Shares issued upon vesting of equity-based awards, net of tax withholding	$ 1	$ 0	(469)	0	0	(468)
Shares issued upon vesting of equity-based awards, net of tax withholding (in shares)	53	0
Shares issued in connection with a business combination	$ 1	$ 0	6,833	0	0	6,834
Shares issued in connection with a business combination (in shares)	133	0
Equity-based compensation	$ 0	$ 0	2,100	0	0	2,100
Ending balance at Dec. 31, 2021	$ 139	$ 14	166,411	94,529	44,101	305,194
Ending balance (in shares) at Dec. 31, 2021	13,852	1,430
Beginning balance at Sep. 30, 2021	$ 133	$ 18	150,825	74,952	28,905	254,833
Beginning balance (in shares) at Sep. 30, 2021	13,277	1,819
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income						65,840
Ending balance at Mar. 31, 2022	$ 139	$ 14	168,095	130,560	50,127	348,935
Ending balance (in shares) at Mar. 31, 2022	13,879	1,430
Beginning balance at Dec. 31, 2021	$ 139	$ 14	166,411	94,529	44,101	305,194
Beginning balance (in shares) at Dec. 31, 2021	13,852	1,430
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	$ 0	0	36,297	6,057	42,354
Distributions to members	0	0	0	(266)	(605)	(871)
Exchange of B shares for A shares	$ 0	$ 0	(574)	0	574	0
Exchange of B shares for A shares (in shares)	0	0
Shares issued upon vesting of equity-based awards, net of tax withholding	$ 0	$ 0	(455)	0	0	(455)
Shares issued upon vesting of equity-based awards, net of tax withholding (in shares)	27	0
Equity-based compensation	$ 0	$ 0	2,713	0	0	2,713
Ending balance at Mar. 31, 2022	$ 139	$ 14	$ 168,095	$ 130,560	$ 50,127	$ 348,935
Ending balance (in shares) at Mar. 31, 2022	13,879	1,430