Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense
Unpaid losses and loss adjustment expenses	$ 824,147	$ 528,842	$ 661,203	$ 482,232
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	573,037	332,229	477,870	305,673
Liability for Unpaid Claims and Claims Adjustment Expense, Net	251,110	196,613	$ 183,333	$ 176,559
Current Year Claims and Claims Adjustment Expense	335,708	290,600
Prior Year Claims and Claims Adjustment Expense	33,216	(4,207)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	368,924	286,393
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	185,257	163,589
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	115,890	102,750
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	301,147	266,339
Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount	271,073	259,678
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 553,074	$ 269,164