Segment Information (Details)	12 Months Ended
	Sep. 30, 2023 USD ($) segment	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	2
Revenue	$ 1,936,310,000	$ 1,744,822,000	$ 1,228,206,000
Income from Operations	18,067,000	217,833,000	148,877,000
Depreciation and amortization	26,789,000	16,296,000	5,411,000
Transaction costs	1,839,000	7,724,000	869,000
Change in fair value of contingent consideration	(1,604,000)	10,380,000	3,249,000
Loss on impairment	147,402,000	0	$ 0
Total assets	1,689,159,000	1,497,428,000
Dealerships
Segment Reporting Information [Line Items]
Loss on impairment	6,500,000
Distribution
Segment Reporting Information [Line Items]
Loss on impairment	140,900,000
Operating Segments | Dealerships
Segment Reporting Information [Line Items]
Revenue	1,755,423,000	1,608,972,000
Income from Operations	163,229,000	211,401,000
Depreciation and amortization	10,731,000	7,628,000
Transaction costs	1,587,000	5,347,000
Change in fair value of contingent consideration	(1,893,000)	10,189,000
Loss on impairment	6,500,000
Total assets	1,435,023,000	1,078,457,000
Operating Segments | Distribution
Segment Reporting Information [Line Items]
Revenue	181,083,000	135,850,000
Income from Operations	(145,154,000)	6,432,000
Depreciation and amortization	16,058,000	8,668,000
Transaction costs	252,000	2,377,000
Change in fair value of contingent consideration	289,000	191,000
Loss on impairment	140,902,000
Total assets	254,164,000	418,971,000
Eliminations
Segment Reporting Information [Line Items]
Revenue	(196,000)	0
Income from Operations	(8,000)	0
Depreciation and amortization	0	0
Transaction costs	0	0
Change in fair value of contingent consideration	0	0
Loss on impairment	0
Total assets	$ (28,000)	$ 0