Quarterly Financial Information (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
Gross written premiums	$ 249,945	$ 227,196	$ 235,032	$ 255,838	$ 221,841	$ 201,296	$ 222,555	$ 249,420	$ 968,011	$ 895,112	$ 836,334
Revenues	225,105	219,870	220,112	212,972	203,575	201,726	199,525	181,046	878,059	785,872	651,039
Net income (loss) from continuing operations	14,742	8,361	8,696	13,695	13,464	15,603	14,652	10,010	45,494	53,729	(6,904)
Net income (loss)	$ 8,520	$ 8,312	$ 8,618	$ 13,440	$ 14,120	$ 15,174	$ 14,454	$ 10,795	$ 38,890	$ 54,543	$ (43,993)
Basic earnings per share - continuing operations (in dollars per share)	$ 0.34	$ 0.20	$ 0.22	$ 0.35	$ 0.35	$ 0.40	$ 0.38	$ 0.26	$ 1.11	$ 1.39	$ (0.18)
Diluted earnings per share - continuing operations (in dollars per share)	0.33	0.19	0.22	0.35	0.34	0.40	0.37	0.25	1.10	1.36	(0.18)
Basic earnings per share (in dollars per share)	0.19	0.19	0.22	0.35	0.36	0.39	0.37	0.28	0.95	1.41	(1.17)
Diluted earnings per share (in dollars per share)	$ 0.19	$ 0.19	$ 0.22	$ 0.34	$ 0.36	$ 0.38	$ 0.36	$ 0.27	$ 0.94	$ 1.38	$ (1.17)