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Intangible Franchise Rights and Goodwill - Narrative (Details)	3 Months Ended		12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) dealership	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Countries and States [Line Items]
Goodwill impairment			$ 0
U.S.
Countries and States [Line Items]
Number of dealerships impaired | dealership		1
Impairment charges	$ 10,400,000	$ 3,000,000.0
Additions through acquisitions			$ 12,100,000	$ 11,500,000
U.K.
Countries and States [Line Items]
Number of dealerships impaired | dealership		7
Impairment charges		$ 5,600,000
Additions through acquisitions				$ 8,400,000

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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