Interim Financial Information (Policies)	3 Months Ended
Interim Financial Information (Policies)	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Consolidated Financial Statements and footnotes thereto that include financial information as of March 31, 2019 and for the three months ended March 31, 2019 and 2018 have been prepared in accordance with accounting principles generally accepted in the U.S. (“U.S. GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements and are unaudited. In the opinion of management, all adjustments of a normal and recurring nature considered necessary for a fair presentation have been included in the accompanying unaudited condensed Consolidated Financial Statements. All business acquisitions completed during the periods presented have been accounted by applying the acquisition method of accounting, and their results of operations are included from the effective dates of the closings of the acquisitions. The allocations of purchase price to the assets acquired and liabilities assumed are assigned and recorded based on estimates of fair value and are subject to change within the purchase price allocation period (generally one year from the respective acquisition date). All intercompany balances and transactions have been eliminated in consolidation.
Business Segment Information	Business Segment Information The Company has three reportable segments: the U.S., which includes the activities of the Company’s corporate office, the U.K. and Brazil. The reportable segments are the business activities of the Company for which discrete financial information is available and for which operating results are regularly reviewed by its chief operating decision maker to allocate resources and assess performance. The Company’s chief operating decision maker is its Chief Executive Officer.
Statements of Cash Flows	Statements of Cash Flows The Company utilizes various credit facilities to finance the purchase of its new and used vehicle inventory. With respect to all new vehicle floorplan borrowings, the manufacturers of the vehicles draft the Company’s credit facilities directly with no cash flow to or from the Company. With respect to borrowings for used vehicle financing in the U.S., the Company finances up to 85% of the value of the used vehicle inventory and the funds flow directly between the Company and the lender. In the U.K. and Brazil, the Company chooses which used vehicles to finance and the borrowings flow directly to the Company from the lender. The Company categorizes the cash flows associated with borrowings and repayments on these various credit facilities as Operating or Financing Activities in its Consolidated Statements of Cash Flows. All borrowings from, and repayments to, lenders affiliated with the vehicle manufacturers (excluding the cash flows from or to manufacturer affiliated lenders participating in the Company’s syndicated lending group under the Revolving Credit Facility (as defined in Note 9, “Credit Facilities”) are presented within Cash Flows from Operating Activities on the Consolidated Statements of Cash Flows. All borrowings from, and repayments to, the syndicated lending group under the Revolving Credit Facility (including the cash flows from or to manufacturer affiliated lenders participating in the facility), as well as borrowings from, and repayments to, the Company’s other credit facilities, are presented within Cash Flows from Financing Activities.
Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The amendment in this update replaces the current incurred loss impairment methodology of recognizing credit losses when a loss is probable, with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to assess credit loss estimates. The standard will be effective for fiscal years beginning after December 15, 2019, with early adoption permitted for periods after December 15, 2018. The Company is currently evaluating the impact that the adoption of the provisions of the ASU will have on its consolidated financial statements, but does not expect the impact of the amendment, if any, in this ASU to be significant. In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The amendment in this update eliminates the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge. Instead, entities will record an impairment charge based on the excess of a reporting unit’s carrying amount over its fair value. This standard should be applied prospectively and is effective for interim and annual periods beginning after December 15, 2019. Earlier application is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the impact of the adoption of the ASU to have a material impact on its consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. The amendment modifies the disclosure requirements on fair value measurements by removing, modifying, or adding certain disclosures. The amendment will be effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. Certain disclosures in this standard, are required to be applied on a retrospective basis and others on a prospective basis. The Company is currently evaluating the potential impact of adopting this guidance on its consolidated financial statements. Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (“Topic 842”), that amends the accounting guidance on leases. The standard establishes a right-of-use (“ROU”) model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. The Company adopted this ASU and all subsequent amendments on January 1, 2019, using the optional transition method applied to leases existing at January 1, 2019, with no restatement of comparative periods. Results for reporting periods beginning after January 1, 2019 are presented under Topic 842, while prior period amounts have not been adjusted and continue to be reported in accordance with the Company’s historical accounting policies under Accounting Standards Codification (“ASC”) Topic 840, Leases (“ASC 840”). The Company elected the package of practical expedients available under the transition guidance within Topic 842, which among other things, permits the Company to carry forward its historical lease classification. The Company also elected other practical expedients under the transition guidance to (i) not record short-term leases on the balance sheet for all asset classes; (ii) not apply hindsight when determining its lease terms or assessing impairment of its ROU assets during transition; and (iii) combine and account for both lease and non-lease components as a single component for all asset classes, except dealership operating assets. For the Company’s dealership operating asset leases, the allocation of the consideration between the lease and non-lease components was based on the estimated fair value of the leased component as of the adoption date. The Company expenses short-term leases, defined as leases with an initial term of 12 months or less, on a straight-line basis over the lease term. Upon adoption of Topic 842, the Company recognized ROU assets and lease liabilities based on the present value of its remaining minimum rental payments for existing operating leases as of the adoption date, utilizing the Company’s applicable incremental borrowing rate also as of the adoption date. The adoption of Topic 842 resulted in the Company recognizing approximately $236.7 million of incremental operating ROU asset with corresponding lease liabilities as of January 1, 2019. Such incremental amounts exclude prepaid rent, favorable lease assets and net unfavorable lease liabilities that were reflected in the Company’s Consolidated Balance Sheets as of December 31, 2018. Additionally, the Company recognized a $6.1 million cumulative-effect adjustment, net of deferred tax impact, to retained earnings as of January 1, 2019. The adjustment to retained earnings resulted from the impairment of certain operating ROU assets subjected to impairment testing under existing accounting guidance for which indicators of impairment existed at the time of the adoption of Topic 842. The Company’s accounting for its finance leases, previously termed as capital leases under ASC 840 remained substantially unchanged. The adoption of Topic 842 had no material impact on the Company’s consolidated statements of operations or consolidated statements of cash flows. For further details, see Note 13, “Leases”. In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The amendments in this update better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. The guidance eliminates the requirement to separately measure and report hedge ineffectiveness and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The guidance also eases the administrative burden of hedge documentation requirements and assessing hedge effectiveness. The amendments to cash flow and net investment hedge relationships should be applied using a modified retrospective approach while the presentation and disclosure requirements are applied prospectively, effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. The Company adopted ASU 2017-12 during the first quarter of 2019. The adoption of this ASU did not impact its consolidated financial statements.
Adoption of ASC Topic 606 - Revenue from Contracts with Customers	The Company’s material revenue streams are the sale of new and used vehicles; arrangement of associated vehicle financing and the sale of service and other insurance contracts; the performance of vehicle maintenance and repair services (including collision restoration); and the sale of vehicle parts.
Derivative Instruments and Risk Management Activities	All of the Company’s interest rate derivative instruments are designated as cash flow hedges. The related gains or losses on these interest rate derivative instruments are deferred in stockholders’ equity as a component of accumulated other comprehensive income (loss). These deferred gains or losses are recognized in income in the period in which the related items being hedged are recognized in expense. Monthly contractual settlements of these swap positions are recognized as “Floorplan interest expense or Other interest expense, net”, in the Company’s accompanying Consolidated Statements of Operations. To the extent that the change in value of a derivative contract does not perfectly offset the change in the value of the items being hedged, that ineffective portion is immediately recognized in other income or expense.
Fair Value Measurements	ASC 820 defines fair value as the price that would be received in the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date; requires disclosure of the extent to which fair value is used to measure financial and non-financial assets and liabilities, the inputs utilized in calculating valuation measurements, and the effect of the measurement of significant unobservable inputs on earnings, or changes in net assets, as of the measurement date; and establishes a three-level valuation hierarchy based upon the transparency of inputs utilized in the measurement and valuation of financial assets or liabilities as of the measurement date: •Level 1 — unadjusted, quoted prices for identical assets or liabilities in active markets; •Level 2 — quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs other than quoted market prices that are observable or that can be corroborated by observable market data by correlation; and •Level 3 — unobservable inputs based upon the reporting entity’s internally developed assumptions that market participants would use in pricing the asset or liability. The Company’s financial instruments consist primarily of cash and cash equivalents, contracts-in-transit and vehicle receivables, accounts and notes receivable, investments in debt and equity securities, accounts payable, credit facilities, long-term debt, and interest rate derivative instruments. The fair values of cash and cash equivalents, contracts-in-transit and vehicle receivables, accounts and notes receivable, accounts payable, and credit facilities approximate their carrying values due to the short-term nature of these instruments and/or the existence of variable interest rates. The Company evaluated its assets and liabilities for those that met the criteria of the disclosure requirements and fair value framework of ASC 820 and identified demand obligations, interest rate derivative instruments, and investment balances in certain financial institutions as having met such criteria. See Note 10, “Long-Term Debt”, for details regarding the fair value of the Company’s long-term debt. The Company periodically invests in unsecured, corporate demand obligations with manufacturer-affiliated finance companies, which bear interest at a variable rate and are redeemable on demand by the Company. Therefore, the Company has classified these demand obligations as Cash and cash equivalents in the accompanying Consolidated Balance Sheets. The Company determined that the valuation measurement inputs of these instruments include inputs other than quoted market prices, that are observable or that can be corroborated by observable data by correlation. Accordingly, the Company has classified these instruments within Level 2 of the hierarchy framework. In addition, the Company maintains an investment balance with certain of the financial institutions in Brazil that provide credit facilities for the financing of new, used, and rental vehicle inventories. The investment balances bear interest at a variable rate and are redeemable by the Company in the future under certain conditions. The Company has classified these investment balances as restricted cash within Prepaid expenses and other current assets within its Consolidated Balance Sheets. The Company determined that the valuation measurement inputs of these instruments include inputs other than quoted market prices that are observable or that can be corroborated by observable data by correlation. Accordingly, the Company has classified these instruments within Level 2 of the hierarchy framework. The Company’s derivative financial instruments are recorded at fair market value.