Organization and Summary of Significant Accounting Policies - Revenue, Defined Contrib. Plans, Advertising, Self-Insurance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dealership Finance and Insurance Sales
Aggregate reserves relating to chargeback activity	$ 26.0	$ 24.9
Defined Contribution Plans
Expense incurred relating to defined contribution plans	24.8	16.8	$ 14.5
Advertising
Net advertising costs	115.3	115.8	102.5
Reimbursement of advertising expense	19.3	18.6	$ 16.6
Self Insurance
Aggregate reserves relating to retained risk	$ 31.3	$ 30.3

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Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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