Segment Information (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2024 USD ($) segment	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	2
Revenue	$ 1,772,630	$ 1,936,310	$ 1,744,822
Income (loss) from operations	64,818	18,067	217,833
Depreciation and amortization	22,187	26,789	16,296
Transaction costs	1,530	1,839	7,724
Change in fair value of contingent consideration	4,248	(1,604)	10,380
Restructuring Costs and Asset Impairment Charges	15,318	147,402
Total assets	1,589,989	1,689,159	1,497,428
Operating Segments | Dealerships
Segment Reporting Information [Line Items]
Revenue	1,616,867	1,755,423	1,608,972
Income (loss) from operations	67,613	163,229	211,401
Depreciation and amortization	12,638	10,731	7,628
Transaction costs	1,334	1,587	5,347
Change in fair value of contingent consideration	4,248	(1,893)	10,189
Restructuring Costs and Asset Impairment Charges	13,049	6,500
Total assets	1,357,650	1,435,023	1,078,457
Operating Segments | Distribution
Segment Reporting Information [Line Items]
Revenue	156,060	181,083	135,850
Income (loss) from operations	(2,750)	(145,154)	6,432
Depreciation and amortization	9,549	16,058	8,668
Transaction costs	196	252	2,377
Change in fair value of contingent consideration	0	289	191
Restructuring Costs and Asset Impairment Charges	2,269	140,902
Total assets	232,351	254,164	418,971
Eliminations
Segment Reporting Information [Line Items]
Revenue	(297)	(196)	0
Income (loss) from operations	(45)	(8)	0
Depreciation and amortization	0	0	0
Transaction costs	0	0	0
Change in fair value of contingent consideration	0	0	0
Restructuring Costs and Asset Impairment Charges	0	0
Total assets	$ (12)	$ (28)	$ 0