Quarterly Results of Operations (Unaudited) - Summary of Unaudited Quarterly Results (Detail) - 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]
Net premiums earned	$ 118,632	$ 118,238	$ 111,204	$ 106,108	$ 101,728	$ 95,208	$ 90,452	$ 92,176	$ 454,182	$ 379,564	$ 411,721
Investment income	1,407	3,852	2,470	3,075	3,122	2,735	2,973	2,502
Total revenues	124,878	125,295	117,972	112,026	108,618	101,774	96,938	99,293	480,171	406,623	438,958
Total operating expenses	102,525	111,079	109,822	87,209	85,448	100,361	83,876	87,403	410,635	357,088	382,193
Operating income	22,353	14,216	8,150	24,817	23,170	1,413	13,062	11,890	69,536	49,535	56,765
Income (loss) from continuing operations	$ 3,929	$ 5,989	$ 2,408	$ 14,829	$ (5,048)	$ (8,696)	$ 6,642	$ 5,983	$ 38,994	$ (5,892)	$ 56,403
Basic	$ 0.15	$ 0.23	$ 0.09	$ 0.58	$ (0.18)	$ (0.34)	$ 0.23	$ 0.21	$ 1.05	$ (0.04)	$ 1.14
Diluted	$ 0.15	$ 0.23	$ 0.09	$ 0.55	$ (0.18)	$ (0.34)	$ 0.23	$ 0.21	$ 1.04	$ (0.04)	$ 1.14