Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense
Unpaid losses and loss adjustment expenses	$ 1,082,126	$ 824,147	$ 760,357	$ 661,203
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	701,715	573,037	482,315	477,870
Liability for Unpaid Claims and Claims Adjustment Expense, Net	380,411	251,110	$ 278,042	$ 183,333
Current Year Claims and Claims Adjustment Expense	429,347	335,708
Prior Year Claims and Claims Adjustment Expense	(6,165)	33,216
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	423,182	368,924
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	195,728	185,257
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	125,085	115,890
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	320,813	301,147
Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount	361,672	271,073
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 720,454	$ 553,074