SCHEDULE IV (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums ceded to other companies									$ 33,800	$ 10,900	$ 9,800
Net premiums earned	$ 141,085	$ 172,693	$ 160,324	$ 151,902	$ 136,632	$ 112,792	$ 125,582	$ 138,112	626,004	513,118	408,387
Property & Casualty
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct gross premiums									0	0	0
Premiums ceded to other companies									56,587	10,015	9,001
Premiums assumed from other companies									692,651	536,072	502,124
Net premiums earned									$ 636,064	$ 526,057	$ 493,123
Percentage of amount assumed to net									109.00%	102.00%	102.00%