Accrual for Loss Contracts Related to Service (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accrual For Loss Contract Related to Service
Beginning balance	$ 752	$ 10,050
Provision		(1,071)	$ 10,050
Reduction for losses realized	(752)	(8,227)
Ending balance	$ 0	$ 752	$ 10,050