Reinsurance - Summary of Premiums Earned and Losses Incurred (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Premiums earned:
Direct	$ 275,044	$ 268,709	$ 808,531	$ 789,317
Assumed	709	312	936	472
Ceded	(25,327)	(31,938)	(79,970)	(92,467)
Net premiums earned	250,426	237,083	729,497	697,322
Losses incurred:
Direct	(2,081)	35,313	12,642	99,122
Assumed	55	(97)	45	69
Ceded	508	(5,469)	(3,810)	(14,486)
Losses incurred, net	$ (1,518)	$ 29,747	$ 8,877	$ 84,705