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Description of Business and Summary of Significant Accounting Policies (Revenue Recognition, Advertising) (Details) - USD ($) $ in Millions | 12 Months Ended |
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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

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- 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 + Details
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- 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 + Details
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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 + Details
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