Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2024 USD ($) segment	Mar. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)
Segment Information [Abstract]
Number of reportable segments | segment			2
Revenue	$ 488,321	$ 524,331	$ 852,334	$ 890,990
Income (loss) from operations	13,855	48,890	20,326	75,426
Depreciation and amortization	5,564	6,360	10,470	12,542
Transaction costs	145	241	724	1,571
Change in fair value of contingent consideration	3,132	1,736	3,704	327
Restructuring and impairment	11,847	0	11,847	0
Total assets	1,712,614	1,770,451	1,712,614	1,770,451	$ 1,689,159
Eliminations
Segment Information [Abstract]
Revenue	(69)	0	(129)	0
Income (loss) from operations	(5)	0	(12)	0
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	(3)	0	(3)	0
Dealerships | Operating Segments
Segment Information [Abstract]
Revenue	450,209	478,348	781,816	805,121
Income (loss) from operations	14,944	48,386	21,887	78,239
Depreciation and amortization	3,066	2,564	5,968	4,938
Transaction costs	104	241	544	1,423
Change in fair value of contingent consideration	3,132	1,626	3,704	83
Restructuring and impairment	10,699	0	10,699	0
Total assets	1,473,755	1,361,097	1,473,755	1,361,097
Distribution | Operating Segments
Segment Information [Abstract]
Revenue	38,181	45,983	70,647	85,869
Income (loss) from operations	(1,084)	504	(1,549)	(2,813)
Depreciation and amortization	2,498	3,796	4,502	7,604
Transaction costs	41	0	180	148
Change in fair value of contingent consideration	0	110	0	244
Restructuring and impairment	1,148	0	1,148	0
Total assets	$ 238,862	$ 409,354	$ 238,862	$ 409,354