CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net (loss) income	$ (39,111,000)	$ 152,611,000	$ 116,413,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	26,789,000	16,296,000	5,411,000
Equity-based compensation	8,962,000	10,013,000	5,741,000
Loss (gain) on asset disposals	221,000	(135,000)	(94,000)
Loss on disposal of a business	750,000	0	0
Loss on impairment	147,402,000	0	0
Loss on extinguishment of debt	0	356,000	0
Non-cash interest expense	10,129,000	3,250,000	659,000
Deferred income tax provision	(23,030,000)	5,741,000	3,728,000
Change in fair value of contingent consideration	(1,604,000)	10,380,000	2,872,000
Loss on equity investments	446,000	1,228,000	0
(Increase) decrease in assets:
Accounts receivable	(10,051,000)	(3,711,000)	(9,531,000)
Inventories	(232,285,000)	(167,183,000)	25,289,000
Prepaid expenses and other current assets	10,308,000	(34,357,000)	(18,924,000)
Other assets	(3,188,000)	(1,940,000)	(173,000)
Increase (decrease) in liabilities:
Accounts payable	197,000	6,424,000	(26,000)
Other payables and accrued expenses	(7,643,000)	4,140,000	4,010,000
Tax receivable agreement liability	(3,227,000)	(67,000)	0
Customer deposits	(14,825,000)	4,401,000	24,048,000
Net cash (used in) provided by operating activities	(129,760,000)	7,447,000	159,423,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(21,251,000)	(11,403,000)	(9,896,000)
Proceeds from disposal of property and equipment	567,000	345,000	233,000
Purchases of equity investments	0	(2,000,000)	0
Cash used for additions to intangible assets	(2,823,000)	(4,246,000)	0
Cash used in acquisitions	(28,882,000)	(459,540,000)	(107,467,000)
Proceeds from disposal of a business	788,000	0	0
Net cash used in investing activities	(51,601,000)	(476,844,000)	(117,130,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net borrowings (payments) from floor plan	219,688,000	152,874,000	(23,497,000)
Proceeds from long-term debt	30,000,000	412,492,000	30,000,000
Payments on long-term debt	(18,338,000)	(88,033,000)	(8,878,000)
Payments of debt issuance costs	0	(9,095,000)	(701,000)
Payments of September Offering costs	0	0	(540,000)
Payments of contingent consideration	(12,574,000)	(371,000)	0
Proceeds from issuance of Class A common stock as part of employee stock purchase plan	2,092,000	0	0
Payments of tax withholdings for equity-based awards	(1,971,000)	(1,628,000)	(802,000)
Dividends and distributions	0	0	(27,070,000)
Distributions to members	(3,603,000)	(9,482,000)	(5,009,000)
Repurchase and retirement of Class A common stock	(1,579,000)	(354,000)	0
Net cash provided by (used in) financing activities	213,715,000	456,403,000	(36,497,000)
Effect of exchange rate changes on cash and restricted cash	9,000	(8,000)	0
Net change in cash and restricted cash	32,363,000	(13,002,000)	5,796,000
Cash and restricted cash at beginning of period	60,947,000	73,949,000	68,153,000
Cash and restricted cash at end of period	93,310,000	60,947,000	73,949,000
Supplemental cash flow disclosures
Cash paid for interest	49,508,000	14,598,000	6,251,000
Cash paid for income taxes	23,322,000	35,229,000	28,537,000
Noncash items
Acquisition purchase price funded by seller notes payable	0	1,126,000	2,056,000
Acquisition purchase price funded by contingent consideration	2,550,000	15,321,000	9,200,000
Acquisition purchase price funded by issuance of Class A common stock	0	14,627,000	1,495,000
Accrued purchase consideration	0	0	1,889,000
Purchase of property and equipment funded by long-term debt	1,122,000	2,087,000	1,820,000
Dividends payable	0	0	1,035,000
Distributions payable	0	0	4,964,000
Initial operating lease right-of-use-assets for adoption of Topic 842	0	0	71,823,000
Acquisition purchase price funded by affiliate financing	10,600,000	0	0
Settlement of affiliate financing with proceeds from sale and leaseback	$ 10,600,000	$ 0	$ 0