Reserves for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves for unpaid losses and loss adjustment expenses, beginning of year	$ 636,013	$ 460,058
Reinsurance recoverable on unpaid losses	94,819	69,099	$ 83,730	$ 69,792
Adoption of new accounting standard for credit losses			0	(282)
Net reserves for unpaid losses and loss adjustment expenses, beginning of year	552,283	390,548
Incurred losses and loss adjustment expenses:
Current year	77,333	56,742
Prior years	(7,073)	(3,009)
Total net losses and loss adjustment expenses incurred	70,260	53,733
Payments:
Current year	1,018	777
Prior years	27,571	21,270
Total payments	28,589	22,047
Reinsurance recoverable on unpaid losses	94,819	69,099	$ 83,730	$ 69,792
Net reserves for unpaid losses and loss adjustment expenses, end of period	593,954	422,234
Gross reserves for unpaid losses and loss adjustment expenses, end of period	$ 688,773	$ 491,333