Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) Segment		Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($) Segment
Segment Information [Abstract]
Number of reportable segments | Segment									1				2
Revenues [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
Commissions and other income									9,932		5,308		5,275
Total revenues									439,169		371,234		318,997
Property and Casualty Insurance [Member]
Revenues [Abstract]
Net premiums earned									432,880		328,145		276,011
Net investment income									22,048		18,095		14,483
Net realized and unrealized gains (losses) on investments									(25,691)		19,686		23,228
Commissions and other income									9,932		5,308		5,275
Total revenues									$ 439,169		$ 371,234		$ 318,997

[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.