Reinsurance - Schedule of Ceded Premiums Earned by Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Effects of Reinsurance
Ceded Premiums Written	$ (61,574)	$ (36,471)	$ (487,627)	$ (422,367)
Increase (Decrease) in Ceded Unearned Premiums	(71,052)	(79,036)	122,616	130,012
Ceded Premiums Earned	(132,626)	(115,507)	(365,011)	(292,355)
Excess of Loss Product Line
Effects of Reinsurance
Ceded Premiums Written	(28,450)	(3,538)	(392,541)	(329,224)
Equipment and Identity Theft Product Line
Effects of Reinsurance
Ceded Premiums Written	(2,375)	(2,606)	(7,126)	(7,275)
Flood Product Line
Effects of Reinsurance
Ceded Premiums Written	(5,897)	(5,559)	(15,136)	(14,319)
Quota Share
Effects of Reinsurance
Ceded Premiums Written	$ (24,852)	$ (24,768)	$ (72,824)	$ (71,549)