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Investments (Net Realized Gains Losses on Disposal) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |
HTM fixed income securities gains | $ 1 | $ 2 | $ 44
HTM fixed income securities losses | (15) | 0 | (1)
Equity securities gains | 24,980 | 23,203 | 5,829
Equity securities losses | (136) | (4,508) | (1,200)
Short term investments gains | 24 | 7 | 2
Short term investments losses | (40) | (10) | (6)
Other investment securities gains | 6 | 0 | 494
Other investment securities losses | (29) | (2,714) | (859)
Net realized investment gains (losses) on disposals | 26,715 | (18,975) | 11,204
Sale of fixed income securities, available-for-sale | 594,743 | 2,030,664 | 1,197,920
Sale of equity securities | 137,294 | 113,339 | 37,960
Fixed Income Securities [Member] |  |  |
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |
AFS securities gains | 6,899 | 5,460 | 10,193
AFS securities losses | (4,975) | (40,415) | (3,292)
Equity Securities [Member] |  |  |
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |
Net realized investment gains (losses) on disposals | $ 24,844 | $ 18,695 | $ 4,629

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