Vehicle Service Agreement Liability Vehicle service agreement liability is presented as components of deferred services fees and accrued expenses and other liabilities in the consolidated balance sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Oct. 12, 2017	Sep. 30, 2017	Dec. 31, 2016
Segment Reporting, Other Significant Reconciling Item [Line Items]
Deferred service fees	$ 45,985	$ 41,113
Accrued expenses and other liabilities	11,327	10,359	$ 2,368
Extended Product Warranty Accrual	43,196	40,794		$ 40,005	$ 38,713
Vehicle service agreement fees [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Deferred service fees	42,933	40,531
Accrued expenses and other liabilities	263	263
Extended Product Warranty Accrual	$ 43,196	$ 40,794