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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, 2016 | Dec. 31, 2015
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Carrying Value | $ 102,397 | $ 77,842
Other Investment Portfolio [Member] |  |
Carrying Value | 102,397 | 77,842
Remaining Commitment | 143,686 | 74,353
Maximum Exposure to Loss | 246,083 | 152,195
Alternative Investments [Member] |  |
Carrying Value | 83,814 | 67,834
Remaining Commitment | 140,286 | 71,153
Maximum Exposure to Loss | 224,100 | 138,987
Private Equity [Member] | Alternative Investments [Member] |  |
Carrying Value | 41,135 | 35,088
Remaining Commitment | 76,774 | 30,204
Maximum Exposure to Loss | 117,909 | 65,292
Private Credit Funds [Member] | Alternative Investments [Member] |  |
Carrying Value | 28,193 | 13,246
Remaining Commitment | 40,613 | 15,129
Maximum Exposure to Loss | 68,806 | 28,375
Real Assets [Member] | Alternative Investments [Member] |  |
Carrying Value | 14,486 | 19,500
Remaining Commitment | 22,899 | 25,820
Maximum Exposure to Loss | 37,385 | 45,320
Other Securities [Member] |  |
Carrying Value | 18,583 | 10,008
Remaining Commitment | 3,400 | 3,200
Maximum Exposure to Loss | $ 21,983 | $ 13,208

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