Revenue From Contracts with Customers Table of Deferred Revenue Liabilities From Contracts with Customers (Rollforward) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Rollforward
Deferred revenue, beginning balance	$ 56,745
Deferred revenue, ending balance	63,797
Customer Contracts
Rollforward
Deferred revenue, beginning balance	43,185
Additions	32,929
Amortizations	28,075
Deferred revenue, ending balance	48,039
Warranty coverage revenue | Customer Contracts
Rollforward
Deferred revenue, beginning balance	28,324
Additions	18,764
Amortizations	12,402
Deferred revenue, ending balance	34,686
Car club revenue | Customer Contracts
Rollforward
Deferred revenue, beginning balance	14,861
Additions	14,165
Amortizations	15,673
Deferred revenue, ending balance	$ 13,353