Unaudited Quarterly Financial Data (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 Financial Information Disclosure [Abstract]
Gross written premiums	$ 72,164	$ 69,546	$ 69,981	$ 63,847	$ 56,943	$ 55,633	$ 57,753	$ 52,862	$ 275,538	$ 223,191	$ 188,478
Revenues	56,904	60,137	54,947	50,126	50,742	47,839	45,508	42,687	222,114	186,776	141,615
Net income	4,448	11,940	10,112	7,287	5,924	4,201	8,495	6,281	33,787	24,901	26,167
Comprehensive income	$ 6,804	$ 9,987	$ 9,096	$ 2,431	$ 7,422	$ 5,840	$ 10,669	$ 7,354	$ 28,318	$ 31,285	$ 25,527
Earnings Per Share, Basic [Abstract]
Basic	$ 0.21	$ 0.57	$ 0.48	$ 0.35	$ 0.28	$ 0.20	$ 0.41	$ 0.30
Diluted earnings per share [Abstract]
Diluted	$ 0.20	$ 0.55	$ 0.47	$ 0.34	$ 0.27	$ 0.20	$ 0.40	$ 0.29