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Store Divestiures (Details) $ in Millions | 3 Months Ended
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Jun. 30, 2018 USD ($) store | Mar. 31, 2018 USD ($) store | Jun. 30, 2017 USD ($) store | Mar. 31, 2017 USD ($) store
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Gain on disposal | $ | $ 1.6 | $ 6.5 | $ 14.8 | $ 4.3
Domestic Stores Divested [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Number of stores divested | 1 | 7 |  |
Import Stores Divested [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Number of stores divested | 2 | 2 | 1 | 1
Premium Luxury Stores Divested [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Number of stores divested |  | 1 |  |
Collision Centers Divested [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Number of stores divested |  | 1 |  |

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- Definition Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2443-110228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2941-110230 + Details
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