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Investments (Fair Value Below Amortized Cost of Gross Unrealized Losses for Fixed Maturity and Equity Securities) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Dec. 31, 2018
Gross unrealized losses with number of securities [Line Items] |  |
Gross Unrealized Losses | $ 230,223 | $ 748,490
% of Total | 100.00% | 100.00%
Less than 20% |  |
Gross unrealized losses with number of securities [Line Items] |  |
Gross Unrealized Losses | $ 208,034 | $ 721,015
% of Total | 90.30% | 96.30%
20% or more for less than six months |  |
Gross unrealized losses with number of securities [Line Items] |  |
Gross Unrealized Losses | $ 20,845 | $ 21,336
% of Total | 9.10% | 2.90%
20% or more for six months or greater |  |
Gross unrealized losses with number of securities [Line Items] |  |
Gross Unrealized Losses | $ 1,344 | $ 6,139
% of Total | 0.60% | 0.80%

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