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Investments (Components of Net Realized and Unrealized Gains (Losses)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gain (Loss) on Securities [Line Items]
Unrealized Gain (Loss) on Investments									$ 1,219	$ (3,098)
Proceeds from Sale of Equity Securities									137,294	113,339	$ 37,960
Net realized investment gains (losses) on disposals									26,715	(18,975)	11,204
OTTI charges									(3,644)	(6,579)	(4,845)
Net realized gains (losses)									23,071	(25,554)	6,359
Unrealized losses recognized in income on equity securities									(8,649)	(29,369)	0
Total net realized and unrealized gains (losses)	$ (873)	$ (2,183)	$ 4,027	$ 13,451	$ (37,935)	$ (4,787)	$ (1,652)	$ (10,549)	14,422	(54,923)	6,359
Unrealized (losses) gains recognized in income on equity securities that were sold in the respective period									(9,868)	(26,271)
Fixed Income Securities [Member]
Gain (Loss) on Securities [Line Items]
Net realized investment gains (losses) on disposals									1,910	(34,953)	6,944
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Net realized investment gains (losses) on disposals									24,844	18,695	4,629
Short-term Investments [Member]
Gain (Loss) on Securities [Line Items]
Net realized investment gains (losses) on disposals									(16)	(3)	(4)
Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Net realized investment gains (losses) on disposals									$ (23)	$ (2,714)	$ (365)

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The cash inflow associated with the sale of equity securities.

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The unrealized gains (losses) on equity securities sold during the period.

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Aggregate net change in unrealized gains or losses on the equity portfolio recognized in net income for the period.

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Amount of unrealized and realized gain (loss) on investment in debt and equity securities.

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Amount of realized and unrealized gain (loss) on investment.

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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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