Investments, Net Realized and Unrealized Gains (Losses) on Investments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Components of net realized and unrealized gains (losses) on investments [Abstract]
Gross gains on available-for-sale fixed income securities during the period	$ 4,151	$ 2,652
Gross losses on available-for-sale fixed income securities during the period	(1,965)	(4,741)
Impairment losses on investments	(82)	(40)
Change in value of limited partnership investments	448	(676)
Gains (losses) on equity securities [Abstract]
Realized gains (losses) on equity securities sold during the period	153	(2,698)
Unrealized gains (losses) on equity securities held at the end of the period	7,804	(22,253)
Realized and unrealized gains (losses) on equity securities during the period	7,957	(24,951)
Net realized and unrealized gains (losses) on investments	10,509	$ (27,756)
Recorded write down to earnings	82
Allowance for credit losses	825		$ 1,035
Reduction in allowance for credit losses	(210)
Undistributed earnings, net of tax	$ 4,201

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