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Inventories - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Lower of cost or net realizable value reserves	$ 8.8	$ 9.7
Reduction in inventory cost for interest received from manufacturers	7.4	10.7
Reduction in new vehicle cost of sales for interest assistance received related to vehicles sold	$ 47.3	$ 49.1	$ 47.3

X

- Definition

Manufacturer floorplan assistance recognized as reduction of cost of sales.

+ References

No definition available.

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- Definition

Manufacturer floorplan assistance recognized as reduction of inventory cost.

+ References

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- References

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X

- Definition

Amount of valuation reserve for inventory.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116846819&loc=d3e3927-108312

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section S99
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
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-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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