Segment Information - Reconciliation, Interest Expense, Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment income	$ (116,230)	$ (6,176)	$ (39,111)
Interest expense – other	(36,183)	(37,050)	(34,557)
Restructuring and impairment	149,678	15,318	147,400
Change in fair value of contingent consideration	2,133	(4,248)	1,604
Equity-based compensation	(10,499)	(8,443)	(8,962)
Transaction costs	(1,547)	(1,530)	(1,839)
Depreciation and amortization	(24,440)	(22,187)	(26,789)
Other expense, net	(1,429)	(14)	(953)
Net loss before income tax benefit	(151,531)	(6,333)	(42,523)
Interest expense – other	36,183	37,050	34,557
Assets	1,403,825	1,589,989
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment income	70,112	82,457	176,373
Dealerships
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment income	68,601	73,227	164,048
Interest expense – other	(36,183)	(37,050)	(34,557)
Interest expense – other	36,183	37,050	34,557
Assets	1,276,806	1,357,638
Dealerships | Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment income	68,601	73,227	164,048
Distribution
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment income	1,511	9,230	12,325
Interest expense – other	0	0	0
Interest expense – other	0	0	0
Assets	127,019	232,351
Distribution | Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment income	$ 1,511	$ 9,230	$ 12,325