SCHEDULE III (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplementary Insurance Information [Abstract]
Deferred acquisition costs, net	$ 62,350	$ 61,022	$ 59,823
Reserves for losses and loss adjustment expenses – gross	464,380	306,641	305,997
Unearned premiums – gross	255,818	222,527	211,954
Net premiums earned	626,004	513,118	408,387
Net investment income (loss)	20,231	76,183	(281,924)
Net losses, and loss adjustment expenses	502,404	380,815	317,097
Amortization of deferred acquisition costs	161,740	134,534	116,207
Other operating expenses	26,356	25,808	23,434
Gross premiums written	$ 692,651	$ 536,072	$ 502,124