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Investments (Other Investment Portfolio by Strategy and the Remaining Commitment Amount Associated With Each Strategy) (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Carrying Value | $ 132,268 | $ 102,397
Other Investment Portfolio [Member] |  |
Carrying Value | 132,268 | 102,397
Remaining Commitment | 220,999 | 143,686
Maximum Exposure to Loss | 353,267 | 246,083
Alternative Investments [Member] |  |
Carrying Value | 115,373 | 83,814
Remaining Commitment | 220,999 | 140,286
Maximum Exposure to Loss | 336,372 | 224,100
Private Equity [Member] | Alternative Investments [Member] |  |
Carrying Value | 52,251 | 41,135
Remaining Commitment | 99,026 | 76,774
Maximum Exposure to Loss | 151,277 | 117,909
Private Credit Funds [Member] | Alternative Investments [Member] |  |
Carrying Value | 37,743 | 28,193
Remaining Commitment | 94,959 | 40,613
Maximum Exposure to Loss | 132,702 | 68,806
Real Assets [Member] | Alternative Investments [Member] |  |
Carrying Value | 25,379 | 14,486
Remaining Commitment | 27,014 | 22,899
Maximum Exposure to Loss | 52,393 | 37,385
Other Securities [Member] |  |
Carrying Value | 16,895 | 18,583
Remaining Commitment | 0 | 3,400
Maximum Exposure to Loss | $ 16,895 | $ 21,983

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