Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Apr. 03, 2017	Dec. 31, 2016	Apr. 29, 2016	Dec. 31, 2015
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid losses and loss adjustment expenses	$ 682,161	$ 122,660		$ 140,855		$ 76,792
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	471,498	9,154		18,724		2,114
Liability for Unpaid Claims and Claims Adjustment Expense, Net	210,663	113,506	$ 40,583	$ 122,131	$ 22,576	$ 74,678
Current Year Claims and Claims Adjustment Expense	296,217	190,031
Prior Year Claims and Claims Adjustment Expense	(2,819)	9,585
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	293,398	199,616
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	160,952	129,927
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	84,497	53,437
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	245,449	183,364
Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount	289,938	75,305
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 392,223	$ 47,355