Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid losses and loss adjustment expenses	$ 629,968	$ 544,249	$ 661,203	$ 482,232
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	434,196	399,814	477,870	305,673
Liability for Unpaid Claims and Claims Adjustment Expense, Net	195,772	144,435	$ 183,333	$ 176,559
Current Year Claims and Claims Adjustment Expense	98,913	77,927
Prior Year Claims and Claims Adjustment Expense	5,634	(681)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	104,547	77,246
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	31,215	34,800
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	60,893	74,570
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	92,108	109,370
Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount	258,550	214,067
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 371,418	$ 330,182