Reinsurance - Summary of Reinsurance Agreements (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	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, 2017	Dec. 31, 2016	Dec. 31, 2015
Premiums Earned, Net [Abstract]
Premiums earned, direct									$ 1,059,973	$ 1,058,545	$ 997,892
Premiums earned, assumed									509	662	1,178
Premiums earned, ceded									(125,735)	(133,981)	(102,848)
Net premiums earned	$ 237,425	$ 237,083	$ 231,136	$ 229,103	$ 235,053	$ 237,376	$ 231,456	$ 221,341	934,747	925,226	896,222
Policyholder Benefits and Claims Incurred, Net [Abstract]
Losses incurred, direct									74,727	273,207	369,680
Losses incurred, assumed									183	1,138	1,552
Losses incurred, ceded									(21,201)	(34,188)	(27,685)
Net losses incurred	$ (30,996)	$ 29,747	$ 27,339	$ 27,619	$ 47,658	$ 60,897	$ 46,590	$ 85,012	53,709	240,157	343,547
Ceded premiums written, net of profit commission									125,726	133,885	55,391
Ceded premiums earned, net of profit commission (1)									125,735	133,981	102,848
Ceded losses incurred									21,201	34,188	27,685
Quota Share Reinsurance Agreements, Excluding Captives
Premiums Earned, Net [Abstract]
Premiums earned, ceded									(120,974)	(125,460)	(88,587)
Policyholder Benefits and Claims Incurred, Net [Abstract]
Losses incurred, ceded									(22,336)	(30,201)	(17,484)
Ceded premiums written, net of profit commission									120,974	125,460	41,233
Ceded premiums earned, net of profit commission (1)									120,974	125,460	88,587
Ceded losses incurred									22,336	30,201	17,484
Ceding commissions									49,321	47,629	30,816
Profit commission									$ 125,629	$ 112,685	$ 112,847