Summary of Significant Accounting Policies - Reinsurance - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Ceded Credit Risk [Line Items]
Amount of allowance for uncollectible amounts on paid recoverables	$ 15,900,000	$ 15,900,000
Reinsurance balances recoverable on unpaid losses and settlement expenses, allowances for uncollectible amounts	8,953,000	$ 8,634,000
Financing Receivable, Allowance for Credit Loss, Writeoff	0
Financing receivable with due date extend beyond one year	$ 0
Threshold period for including reinsurance receivables in the allowance for uncollectible amounts	1 year
Maximum
Ceded Credit Risk [Line Items]
Financing Receivable, Allowance for Credit Loss, Recovery	$ 100,000