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INVESTMENTS - Securities narrative (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule Of Available For Sale Securities [Line Items] |  |
Fair Value | $ 12,622,006 | $ 11,397,114
Unrealized Losses | (91,000) | (197,000)
Equity securities | 635,511 | 638,744
Non-U.S. government |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair Value | 806,299 | 565,834
Unrealized Losses | (9,523) | (49,654)
Non-U.S. government | Eurozone |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair Value | 185,000 | 28,000
CMBS |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair Value | 777,728 | 666,237
Unrealized Losses | $ (3,125) | $ (3,564)
CMBS | Weighted Average |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Subordination percentage input for determining credit losses | 29.00% | 36.00%
Non-Agency RMBS |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair Value | $ 46,831 | $ 56,921
Unrealized Losses | (799) | (2,023)
Non-Agency RMBS | Prime |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair Value | 34,000 | 40,000
Non-Agency RMBS | Alt A |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair Value | 8,000 | 10,000
Equity securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Unrealized Losses | $ (1,883) | $ (12,068)

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- Definition This item represents the current level of subordination of the entity's receipt of consideration should the assets underlying the security be liquidated when the level of subordination was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are other than temporarily impaired and the amount of such impairment determined to be related to credit loss recognized in earnings. + References No definition available. + Details
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