Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Gross written premiums	$ 112,137	$ 97,984	$ 94,947	$ 84,626	$ 72,164	$ 69,546	$ 69,981	$ 63,847	$ 389,694	$ 275,538	$ 223,191
Revenues	92,804	78,327	72,572	72,185	56,904	60,137	54,947	50,126	315,888	222,114	186,776
Net income	17,853	12,976	13,767	18,720	4,448	11,940	10,112	7,287	63,316	33,787	24,901
Comprehensive income	$ 16,050	$ 16,218	$ 20,322	$ 25,500	$ 6,804	$ 9,987	$ 9,096	$ 2,431	$ 78,090	$ 28,318	$ 31,285
Earnings Per Share, Basic [Abstract]
Basic	$ 0.81	$ 0.60	$ 0.65	$ 0.88	$ 0.21	$ 0.57	$ 0.48	$ 0.35	$ 2.94	$ 1.60	$ 1.19
Diluted earnings per share [Abstract]
Diluted	$ 0.79	$ 0.58	$ 0.63	$ 0.86	$ 0.20	$ 0.55	$ 0.47	$ 0.34	$ 2.86	$ 1.56	$ 1.16