Unaudited Selected 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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Insurance premiums written and contract deposits	$ 311,216	$ 338,097	$ 301,722	$ 284,008	$ 300,416	$ 318,355	$ 311,614	$ 296,732	$ 315,917	$ 351,534	$ 311,879	$ 283,169
Total revenues	278,535	311,318	306,257	295,489	302,993	289,817	291,436	287,304	282,873	291,176	283,558	271,303	$ 1,191,599	$ 1,171,550	$ 1,128,910
Net income	$ (20,257)	$ 12,528	$ 5,917	$ 20,155	$ 125,329	$ 26,551	$ 2,261	$ 15,318	$ 19,823	$ 26,923	$ 11,866	$ 25,153	$ 18,343	$ 169,459	$ 83,765
Basic
Net income - basic (in usd per share)	$ (0.49)	$ 0.30	$ 0.14	$ 0.49	$ 3.03	$ 0.64	$ 0.05	$ 0.37	$ 0.48	$ 0.66	$ 0.29	$ 0.61	$ 0.44	$ 4.10	$ 2.04
Shares of common stock - weighted average basic (in shares)	41,596,000,000	41,683,000,000	41,600,000,000	41,497,000,000	41,419,000,000	41,433,000,000	41,368,000,000	41,135,000,000	41,093,000,000	41,092,000,000	41,082,000,000	41,297,000,000	41,570,492	41,364,546	41,158,349
Diluted
Net income - diluted (in usd per share)	$ (0.49)	$ 0.30	$ 0.14	$ 0.48	$ 3.00	$ 0.64	$ 0.05	$ 0.37	$ 0.48	$ 0.65	$ 0.29	$ 0.61	$ 0.44	$ 4.08	$ 2.02
Shares of common stock and equivalent shares - weighted average diluted (in shares)	41,911,000,000	41,850,000,000	41,735,000,000	41,653,000,000	41,718,000,000	41,575,000,000	41,493,000,000	41,342,000,000	41,482,000,000	41,347,000,000	41,314,000,000	41,492,000,000	41,894,232	41,564,979	41,475,516
TCJA effect, earnings per share, basic (in usd per share)					$ 2.39
TCJA effect, earnings per share, diluted (in usd per share)					$ 2.37