Interim Financial Information - Adoption of ASC Topic 606, "Revenue from Contract with Customers" (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Impact of ASC 606 cumulative adjustment	$ 11,397
ASU 2014-09 | Parts and Service Sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Impact of ASC 606 cumulative adjustment		$ 4,800
ASU 2014-09 | Finance and Insurance Sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Impact of ASC 606 cumulative adjustment		$ 6,600