Schedule IV (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
Direct Premiums Written	$ 989,525	$ 708,252	$ 548,916
Ceded Premiums Written	447,329	262,340	183,808
Assumed Premiums Written	51,323	(96)	20,820
Premiums Written, Net	$ 593,519	$ 445,816	$ 385,928
premiums assumed as percentage of net premiums	8.60%	0.00%	5.40%