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Description of Business and Summary of Significant Accounting Policies (Revenue Recognition, Advertising) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Advertising [Abstract]
Advertising expense, net	$ 192.8	$ 196.7	$ 188.5
Manufacturer advertising reimbursements	65.0	58.5	56.4
Chargeback Reserves [Member]
Revenue Recognition [Abstract]
Chargeback liabilities	$ 120.8	$ 116.8	$ 97.3	$ 84.9

X

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 720
-SubTopic 35
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848

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X

- Definition

Total amount received by an entity from a vendor under a cooperative advertising arrangement that has been offset against advertising expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 50
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=68069731&loc=d3e63872-111659

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 705
-SubTopic 20
-Section 25
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=68067574&loc=SL51760044-203187

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- References

No definition available.

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- References

No definition available.

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- Definition

Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

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