Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Quarterly Results of Operations (Unaudited) [Abstract]
Net premiums earned	$ 118,671	$ 96,807	$ 111,940	$ 105,462	$ 97,075	$ 89,100	$ 67,996	$ 73,974	$ 432,880	[1]	$ 328,145	[1]	$ 276,011	[1]
Net investment income	6,038	5,578	5,796	4,636	5,661	4,027	4,716	3,692	22,048		18,095		14,483
Net realized and unrealized gains (losses) on investments	(20,096)	2,373	(3,435)	(4,533)	4,152	5,944	3,296	6,294	(25,691)		19,686		23,228
Losses and loss expenses incurred	101,537	94,540	77,488	72,298	66,492	60,673	71,754	48,599	345,864		247,518		186,481
Net income (loss)	$ (24,567)	$ (12,325)	$ 2,487	$ 330	$ 16,476	$ 7,434	$ (12,343)	$ 6,756	$ (34,075)		$ 18,323		$ 28,945
Net income (loss) per share (in dollars per share)	$ (1.65)	$ (0.82)	$ 0.17	$ 0.02	$ 1.10	$ 0.49	$ (0.82)	$ 0.45	$ (2.28)		$ 1.21		$ 1.92

[1] Included in Ceded to Other Companies is $0, $0 and $86 for 2018, 2017 and 2016, respectively, relating to retrocessions associated with premiums assumed from other companies. percentage of Amount Assumed to Net above considers the impact of this retrocession.