Organization and Summary of Significant Accounting Policies - Impairment Testing (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2023 USD ($) reporting_unit	Sep. 30, 2023 reporting_unit	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			4
Number of reporting units | reporting_unit	4
Goodwill	$ 2,234,900,000		$ 2,234,900,000	$ 2,154,700,000	$ 2,124,100,000
Retail automotive dealership
Segment Reporting Information [Line Items]
Number of reportable segments | segment			1
Number of reporting units | reporting_unit	2	6
Goodwill	$ 1,664,000,000		$ 1,664,000,000	1,617,600,000	1,622,200,000
Retail commercial truck dealership
Segment Reporting Information [Line Items]
Number of reporting units | segment			1
Goodwill	494,300,000		$ 494,300,000	$ 462,300,000	$ 422,300,000
Non-Automotive Investments
Segment Reporting Information [Line Items]
Goodwill	$ 0		$ 0