Revenue From Contracts with Customers Table of Deferred Assets Related to Revenue From Contracts with Customers (Rollforward) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Table of Deferred Assets Related to Revenue From Contracts with Customers [Roll Forward]
Deferred acquisition costs, beginning balance	$ 147,162
Deferred acquisition costs, ending balance	143,146
Customer Contracts [Member]
Table of Deferred Assets Related to Revenue From Contracts with Customers [Roll Forward]
Deferred acquisition costs, beginning balance	13,393
Additions	4,453
Amortizations	6,289
Deferred acquisition costs, ending balance	11,557
Warranty coverage revenue | Customer Contracts [Member]
Table of Deferred Assets Related to Revenue From Contracts with Customers [Roll Forward]
Deferred acquisition costs, beginning balance	2,249
Additions	96
Amortizations	373
Deferred acquisition costs, ending balance	1,972
Car club revenue | Customer Contracts [Member]
Table of Deferred Assets Related to Revenue From Contracts with Customers [Roll Forward]
Deferred acquisition costs, beginning balance	11,144
Additions	4,357
Amortizations	5,916
Deferred acquisition costs, ending balance	$ 9,585