Reinsurance - Schedule of Ceded Premiums Earned by Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Effects of Reinsurance [Line Items]
Ceded Premiums Written	$ (385,829)	$ (350,833)	$ (426,053)	$ (385,896)
Increase (Decrease) in Ceded Unearned Premiums	267,494	248,867	193,668	209,048
Ceded Premiums Earned	(118,335)	(101,966)	(232,385)	(176,848)
Excess of Loss Product Line
Effects of Reinsurance [Line Items]
Ceded Premiums Written	(350,230)	(315,457)	(364,091)	(325,686)
Equipment and Identity Theft Product Line
Effects of Reinsurance [Line Items]
Ceded Premiums Written	(2,631)	(2,596)	(4,751)	(4,669)
Flood Product Line
Effects of Reinsurance [Line Items]
Ceded Premiums Written	(5,568)	(5,369)	(9,239)	(8,760)
Quota Share
Effects of Reinsurance [Line Items]
Ceded Premiums Written	$ (27,400)	$ (27,411)	$ (47,972)	$ (46,781)