Unpaid Loss and Loss Adjustment Expenses Vehicle Service Agreements (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Liability for Claims and Claims Adjustment Expense [Line Items]
Vehicle service agreements	$ 2,777	$ 3,055	$ 2,915
Other Insurance Product Line [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Current year	3,927	4,153
Prior years	0	0
Current year	4,002	3,920
Prior years	$ (63)	$ (153)
Vehicle service agreements			$ 2,915	$ 2,975