Effects of Reinsurance on Premiums (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance [Abstract]
Direct Premiums Written	$ 989,525	$ 708,252	$ 548,916
Assumed Premiums Written	51,323	(96)	20,820
Ceded Premiums Written	(447,329)	(262,340)	(183,808)
Premiums Written, Net	593,519	445,816	385,928
Increase (Decrease) in Direct Unearned Premiums	(49,386)	(57,759)	(65,300)
Increase (Decrease) in Assumed Unearned Premiums	(5,439)	16,432	(221)
Increase (Decrease) in Ceded Unearned Premiums	46,796	52,442	15,551
Increase (Decrease) in Unearned Premiums	(8,029)	11,115	(49,970)
Direct Premiums Earned, Property and Casualty	940,139	650,493	483,616
Assumed Premiums Earned, Property and Casualty	45,884	16,336	20,599
Ceded Premiums Earned	(400,533)	(209,898)	(168,257)
Premiums Earned, Net	585,490	456,931	335,958
Direct Losses and LAE Incurred	863,928	335,542	188,270
Assumed Losses and LAE Incurred	60,836	3,747	7,861
Ceded Losses and LAE Incurred	(559,229)	(40,936)	(13,023)
Net Losses and LAE Incurred	$ 365,535	$ 298,353	$ 183,108