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Business and Summary of Significant Accounting Policies and Estimates - Business and Credit Risk Concentrations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Concentration Risk [Line Items]
Amounts due	$ 227.9	$ 197.2
Due from Manufacturers
Concentration Risk [Line Items]
Amounts due	$ 124.0	$ 105.1
Toyota | Due from Manufacturers
Concentration Risk [Line Items]
Percentage of Company's new vehicle sales volume more than which no other manufacturer accounted for	24.70%
Volkswagen | Due from Manufacturers
Concentration Risk [Line Items]
Percentage of Company's new vehicle sales volume more than which no other manufacturer accounted for	14.10%
BMW | Due from Manufacturers
Concentration Risk [Line Items]
Percentage of Company's new vehicle sales volume more than which no other manufacturer accounted for	12.00%
Honda | Due from Manufacturers
Concentration Risk [Line Items]
Percentage of Company's new vehicle sales volume more than which no other manufacturer accounted for	10.70%
Ford | Due from Manufacturers
Concentration Risk [Line Items]
Percentage of Company's new vehicle sales volume more than which no other manufacturer accounted for	10.40%

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- Definition

Percentage of Company's new vehicle sales volume more then which no other manufacturer accounted for.

+ References

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Amount, before allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4531-111522

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