Investments - Net Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	$ 75,050	$ 72,862	$ 73,988
Less investment expenses	(6,188)	(4,969)	(5,118)
Net investment income	68,862	67,893	68,870
Debt Securities
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	60,624	59,755	60,364
Equity Securities
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	11,787	9,728	9,950
Cash and Short-term Investments
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	$ 2,639	$ 3,379	$ 3,674