Investments (Schedule of Components of Net Realized and Unrealized Gains and Losses Excluding OTTI (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	$ 2,615	$ 2,883	$ 6,715	$ 6,327
OTTI benefit (expense)	(4,333)	(971)	(27,296)	(1,075)
Net realized gains (losses)	6,948	1,912	(20,581)	5,252
Total unrealized gains (losses) recognized in income on equity securities	5,701	2,115	(11,436)	12,226
Total net realized and unrealized investment gains (losses)	12,649	4,027	(32,017)	17,478
Increase in net realized and unrealized investment gains	8,600
Fixed Income Securities [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	2,300	2,061	6,576	3,204
Commercial Mortgage Loans [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	1	0	1	0
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	0	851	(3)	3,131
Short-Term Investments [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	314	1	146	15
Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	$ 0	$ (30)	$ (5)	$ (23)

Realized and unrealized investment change between the current and prior 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 unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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

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The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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