Reinsurance - Summary of Reinsurance Agreements (Details) - USD ($) $ 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
Premiums Earned, Net [Abstract]
Premiums earned, direct									$ 1,084,748	$ 1,059,973	$ 1,058,545
Premiums earned, assumed									1,805	509	662
Premiums earned, ceded									(111,391)	(125,735)	(133,981)
Net premiums earned	$ 245,665	$ 250,426	$ 246,964	$ 232,107	$ 237,425	$ 237,083	$ 231,136	$ 229,103	975,162	934,747	925,226
Policyholder Benefits and Claims Incurred, Net [Abstract]
Losses incurred, direct									43,060	74,727	273,207
Losses incurred, assumed									331	183	1,138
Losses incurred, ceded									(6,829)	(21,201)	(34,188)
Net losses incurred	$ 27,685	$ (1,518)	$ (13,455)	$ 23,850	$ (30,996)	$ 29,747	$ 27,339	$ 27,619	36,562	53,709	240,157
Ceded losses incurred									6,829	21,201	34,188
Quota Share Reinsurance Agreements, Excluding Captives
Policyholder Benefits and Claims Incurred, Net [Abstract]
Losses incurred, ceded									(6,543)	(22,336)	(30,201)
Ceded premiums written and earned, net of profit commission									108,337	120,974	125,460
Ceded losses incurred									6,543	22,336	30,201
Ceding commissions									51,201	49,321	47,629
Profit commission									$ 147,667	$ 125,629	$ 112,685