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Investments (Net Realized Gains Losses on Disposal) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |
HTM fixed income securities gains | $ 2 | $ 44 | $ 3
HTM fixed income securities losses | 0 | (1) | (1)
Equity securities gains | 23,203 |  |
Equity securities losses | (4,508) |  |
Short term investments gains | (7) | (2) | 0
Short term investments losses | 10 | 6 | (13)
Other investment securities gains | 0 | 494 | 3
Other investment securities losses | (2,714) | (859) | (4)
Net realized investment (losses) gains on disposals | (18,975) | 11,204 | 3,562
Sale of fixed income securities, available-for-sale | 2,030,664 | 1,197,920 | 926,470
Sale of equity securities | 113,339 |  |
Sale of equity securities, available-for-sale |  | 37,960 | 119,617
Fixed Income Securities [Member] |  |  |
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |
AFS securities gains | 5,460 | 10,193 | 7,741
AFS securities losses | (40,415) | (3,292) | (11,411)
Equity Securities [Member] |  |  |
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |
AFS securities gains |  | 5,829 | 8,108
AFS securities losses |  | (1,200) | (864)
Net realized investment (losses) gains on disposals | $ 18,695 | $ 4,629 | $ 7,244

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