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Multiemployer Pension Plans (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($) store agreements | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Multiemployer Plans [Line Items] |  |  |  |
Total contributions | [1] | $ 1.6 | $ 1.5 | $ 1.4
Automotive Industries Pension Plan [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
EIN |  | 941133245 |  |
Multiemployer plan number |  | 001 |  |
Pension protection act zone status |  | Red | Red |
Total contributions | [1] | $ 1.3 | $ 1.1 | 1.0
Surcharge imposed |  | Yes |  |
Number of collective-bargaining arrangements that require contributions to the Plan | agreements |  | 2 |  |
Other funds [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Total contributions | [1] | $ 0.3 | $ 0.4 | $ 0.4
Dealerships [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Number of stores | store |  | 253 |  |
Dealerships [Member] | Multiemployer Plans, Pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Number of stores | store |  | 5 |  |
[1] | Our stores were not listed in the Automotive Industries Pension Plan’s Form 5500 as providing more than 5% of the total contributions for the plan years ended December 31, 2016 or 2015.

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- Definition The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation 12B -Number 240 -Section 12b -Subsection 1 + Details
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- Definition Amount of contributions made to multiemployer plan by employer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947 + Details
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- Definition Three digit plan number for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
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- Definition Indicate the multiemployer plan's certified zone status as currently required by the Pension Protection Act of 2006 or a subsequent amendment thereof. The zone status categories are red (critical status), orange (seriously endangered), yellow (endangered), and green (none of the above). The acceptable values are "red", "orange", "yellow", "green", "other", and "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Indicate whether the employer paid a surcharge to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "yes", and "NA". + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947 + Details
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