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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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