Deferred Acquisition Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Acquisition Costs [Line Items]
Beginning balance, net	$ (6,899)	$ (6,054)	$ (6,899)	$ (6,241)	$ (6,662)	$ (6,325)	$ (5,827)
Additions	1,047	1,255	3,545	3,572
Amortization	810	1,068	2,971	3,158
Balance at September 30, net	$ 6,899	$ 6,054	$ 6,899	$ 6,241