Investments, Net Realized and Unrealized Gains (Losses) on Investments (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Components of net realized and unrealized gains (losses) on investments [Abstract]
Gross gains on available-for-sale fixed income securities during the period	$ 2,561	$ 4,132	$ 5,213	$ 7,303
Gross losses on available-for-sale fixed income securities sold during the period	(149)	(3,154)	(4,890)	(6,681)
Impairment losses on investments	(418)	(86)	(458)	(346)
Change in value of limited partnership investments	(587)	314	(1,263)	722
Gains (losses) on equity securities [Abstract]
Realized gains (losses) on equity securities sold during the period	(6,511)	(265)	(9,209)	51
Unrealized gains (losses) on equity securities held at the end of the period	15,719	1,948	(6,534)	7,867
Realized and unrealized gains (losses) on equity securities during the period	9,208	1,683	(15,743)	7,918
Net realized and unrealized gains (losses) on investments	10,615	$ 2,889	(17,141)	$ 8,916
Recorded write down to earnings	$ 400		500
Undistributed earnings, net of tax			$ 3,989

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