Revenue Recognition	9 Months Ended
Sep. 30, 2018
Disaggregation of Revenue [Abstract]
Revenue Recognition	Revenue Recognition The following describes our major product lines, which represent the disaggregation of our revenues to transactions that are similar in nature, amount, timing, uncertainties and economic factors. New Retail Vehicle and Used Retail Vehicle Sales Revenue from the retail sale of a vehicle is recognized at a point in time, as all performance obligations are satisfied when a contract is signed by the customer, financing has been arranged or collectibility is probable and the control of the vehicle is transferred to the customer. The transaction price for a retail vehicle sale is specified in the contract with the customer and includes all cash and non-cash consideration. In a retail vehicle sale, customers often trade in their current vehicle. The trade-in is measured at its stand-alone selling price in the contract, utilizing various third-party pricing sources. There are no other non-cash forms of consideration related to retail sales. All vehicle rebates are applied to the vehicle purchase price at the time of the sale and are therefore incorporated into the price of the contract at the time of the exchange. We do not allow the return of new or used vehicles, except where mandated by state law. Service, Body and Parts Sales Revenue from service, body and parts sales is recognized upon the transfer of control of the parts or service to the customer. We allow for customer returns on sales of our parts inventory up to 30 days after the sale. Most parts returns generally occur within one to two weeks from the time of sale and are not significant. We are the obligor on our lifetime oil contracts. Revenue is allocated to these performance obligations and is recognized over time as services are provided to the customer. The amount of revenue recognized is calculated, net of cancellations, using an input method, which most closely depicts performance of the contracts. Our contract liability balances were $144.9 million and $126.1 million as of September 30, 2018, and December 31, 2017, respectively; and we recognized $5.2 million and $16.9 million of revenue in the three and nine months ended September 30, 2018, related to our opening contract liability balance. Finance and Insurance Sales Revenue from finance and insurance sales is recognized, net of estimated charge-backs, at the time of the sale of the related vehicle. As a part of the vehicle sale, we seek to arrange financing for customers and sell a variety of add-ons, such as extended warranty service contracts. These products are inherently attached to the governing vehicle and performance of the obligation cannot be performed without the underlying sale of the vehicle. We act as an agent in the sale of these contracts as the pricing is set by the third-party provider, and our commission is preset. A portion of the transaction price related to sales of finance and insurance contracts is considered variable consideration and is estimated and recognized upon the sale of the contract under the new standard. We recognized a $9.2 million asset associated with future estimated variable consideration on January 1, 2018, related to contracts sold on or before December 31, 2017. Our contract asset balance was $9.2 million as of September 30, 2018, and is included in trade receivables and other non-current assets.

Revenue Recognition

The following describes our major product lines, which represent the disaggregation of our revenues to transactions that are similar in nature, amount, timing, uncertainties and economic factors.

New Retail Vehicle and Used Retail Vehicle Sales

Revenue from the retail sale of a vehicle is recognized at a point in time, as all performance obligations are satisfied when a contract is signed by the customer, financing has been arranged or collectibility is probable and the control of the vehicle is transferred to the customer. The transaction price for a retail vehicle sale is specified in the contract with the customer and includes all cash and non-cash consideration. In a retail vehicle sale, customers often trade in their current vehicle. The trade-in is measured at its stand-alone selling price in the contract, utilizing various third-party pricing sources. There are no other non-cash forms of consideration related to retail sales. All vehicle rebates are applied to the vehicle purchase price at the time of the sale and are therefore incorporated into the price of the contract at the time of the exchange. We do not allow the return of new or used vehicles, except where mandated by state law.

Service, Body and Parts Sales

Revenue from service, body and parts sales is recognized upon the transfer of control of the parts or service to the customer. We allow for customer returns on sales of our parts inventory up to 30 days after the sale. Most parts returns generally occur within one to two weeks from the time of sale and are not significant.

We are the obligor on our lifetime oil contracts. Revenue is allocated to these performance obligations and is recognized over time as services are provided to the customer. The amount of revenue recognized is calculated, net of cancellations, using an input method, which most closely depicts performance of the contracts. Our contract liability balances were $144.9 million and $126.1 million as of September 30, 2018, and December 31, 2017, respectively; and we recognized $5.2 million and $16.9 million of revenue in the three and nine months ended September 30, 2018, related to our opening contract liability balance.

Finance and Insurance Sales

Revenue from finance and insurance sales is recognized, net of estimated charge-backs, at the time of the sale of the related vehicle. As a part of the vehicle sale, we seek to arrange financing for customers and sell a variety of add-ons, such as extended warranty service contracts. These products are inherently attached to the governing vehicle and performance of the obligation cannot be performed without the underlying sale of the vehicle. We act as an agent in the sale of these contracts as the pricing is set by the third-party provider, and our commission is preset. A portion of the transaction price related to sales of finance and insurance contracts is considered variable consideration and is estimated and recognized upon the sale of the contract under the new standard. We recognized a $9.2 million asset associated with future estimated variable consideration on January 1, 2018, related to contracts sold on or before December 31, 2017. Our contract asset balance was $9.2 million as of September 30, 2018, and is included in trade receivables and other non-current assets.