Reinsurance - Schedule of Ceded Premiums Earned by Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Effects of Reinsurance [Line Items]
Ceded Premiums Written	$ (350,833)	$ (187,487)	$ (385,896)	$ (196,163)
Increase (Decrease) in Ceded Unearned Premiums	248,867	137,081	209,048	100,625
Ceded Premiums Earned	(101,966)	(50,406)	(176,848)	(95,538)
Excess of Loss Product Line
Effects of Reinsurance [Line Items]
Ceded Premiums Written	(342,868)	(177,970)	(372,467)	(182,027)
Equipment and Identity Theft Product Line
Effects of Reinsurance [Line Items]
Ceded Premiums Written	(2,596)	(2,201)	(4,669)	(3,777)
Flood Product Line
Effects of Reinsurance [Line Items]
Ceded Premiums Written	(5,369)	(4,920)	(8,760)	(7,963)
Novation of Auto Policies [Member]
Effects of Reinsurance [Line Items]
Ceded Premiums Written	$ 0	$ (2,396)	$ 0	$ (2,396)