Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) segment	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)
Segment Information [Abstract]
Number of reportable segments | segment			2
Revenue	$ 542,441	$ 594,339	$ 1,394,775	$ 1,485,329
Income (loss) from operations	39,999	60,080	60,325	135,506
Depreciation and amortization	5,785	6,584	16,255	19,126
Transaction costs	242	97	966	1,668
Change in fair value of contingent consideration	214	436	3,918	763
Restructuring and impairment	0	0	11,847	0
Total assets	1,635,880	1,771,317	1,635,880	1,771,317	$ 1,689,159
Eliminations
Segment Information [Abstract]
Revenue	(120)	(153)	(249)	(153)
Income (loss) from operations	(11)	(7)	(23)	(7)
Depreciation and amortization	0	0	0	0
Transaction costs	0	0	0	0
Change in fair value of contingent consideration	0	0	0	0
Restructuring and impairment	0	0	0	0
Total assets	(20)	(25)	(20)	(25)
Dealerships | Operating Segments
Segment Information [Abstract]
Revenue	497,793	543,312	1,279,609	1,348,433
Income (loss) from operations	38,804	59,699	60,691	137,938
Depreciation and amortization	3,276	2,768	9,244	7,706
Transaction costs	233	9	777	1,432
Change in fair value of contingent consideration	214	390	3,918	474
Restructuring and impairment	0	0	10,699	0
Total assets	1,396,048	1,368,783	1,396,048	1,368,783
Distribution | Operating Segments
Segment Information [Abstract]
Revenue	44,768	51,180	115,415	137,049
Income (loss) from operations	1,206	388	(343)	(2,425)
Depreciation and amortization	2,509	3,816	7,011	11,420
Transaction costs	9	88	189	236
Change in fair value of contingent consideration	0	46	0	289
Restructuring and impairment	0	0	1,148	0
Total assets	$ 239,852	$ 402,559	$ 239,852	$ 402,559