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Investments (Other Investment Portfolio by Strategy and the Remaining Commitment Amount Associated With Each Strategy) (Details) (USD $) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2011 | Sep. 30, 2010 | Sep. 30, 2011 | Sep. 30, 2010 | Dec. 31, 2010
Carrying Value | $ 135,560,000 |  | $ 135,560,000 |  | $ 137,865,000
Decrease in other investments |  |  | (2,300,000) |  |
Net investment income earned | 35,786,000 | 32,986,000 | 118,604,000 | 104,237,000 |
Energy/Power Generation [Member] | Alternative Investments [Member] |  |  |  |  |
Carrying Value | 30,792,000 |  | 30,792,000 |  | 35,560,000
Remaining Commitment | 10,296,000 |  | 10,296,000 |  |
Net investment income earned | 1,760,000 | 409,000 | 7,599,000 | 3,440,000 |
Secondary Private Equity Member | Alternative Investments [Member] |  |  |  |  |
Carrying Value | 29,077,000 |  | 29,077,000 |  | 26,709,000
Remaining Commitment | 11,047,000 |  | 11,047,000 |  |
Net investment income earned | 1,179,000 | 240,000 | 5,895,000 | 3,924,000 |
Private Equity [Member] | Alternative Investments [Member] |  |  |  |  |
Carrying Value | 21,067,000 |  | 21,067,000 |  | 21,601,000
Remaining Commitment | 6,637,000 |  | 6,637,000 |  |
Net investment income earned | 1,640,000 | 543,000 | 5,398,000 | 1,350,000 |
Distressed Debt [Member] | Alternative Investments [Member] |  |  |  |  |
Carrying Value | 19,285,000 |  | 19,285,000 |  | 20,432,000
Remaining Commitment | 3,169,000 |  | 3,169,000 |  |
Net investment income earned | (153,000) | 472,000 | 1,241,000 | 1,195,000 |
Real Estate Strategy [Member] | Alternative Investments [Member] |  |  |  |  |
Carrying Value | 14,033,000 |  | 14,033,000 |  | 14,192,000
Remaining Commitment | 10,602,000 |  | 10,602,000 |  |
Net investment income earned | 35,000 | 303,000 | 1,485,000 | (2,056,000) |
Mezzanine Financing [Member] | Alternative Investments [Member] |  |  |  |  |
Carrying Value | 9,993,000 |  | 9,993,000 |  | 10,230,000
Remaining Commitment | 15,910,000 |  | 15,910,000 |  |
Net investment income earned | (133,000) | 377,000 | 928,000 | 3,006,000 |
Venture Capital [Member] | Alternative Investments [Member] |  |  |  |  |
Carrying Value | 7,909,000 |  | 7,909,000 |  | 6,386,000
Remaining Commitment | 900,000 |  | 900,000 |  |
Net investment income earned | 125,000 | 15,000 | 1,448,000 | 263,000 |
Other Securities [Member] |  |  |  |  |
Carrying Value | 3,404,000 |  | 3,404,000 |  | 2,755,000
Remaining Commitment | 2,096,000 |  | 2,096,000 |  |
Other Investments [Member] |  |  |  |  |
Carrying Value | 135,560,000 |  | 135,560,000 |  | 137,865,000
Remaining Commitment | 60,657,000 |  | 60,657,000 |  |
Net investment income earned | 4,494,000 | 2,400,000 | 24,082,000 | 11,216,000 |
Additional contributions |  |  | 11,800,000 |  |
Alternative Investments [Member] |  |  |  |  |
Carrying Value | 132,156,000 |  | 132,156,000 |  | 135,110,000
Remaining Commitment | 58,561,000 |  | 58,561,000 |  |
Distributions from alternative investments |  |  | 37,900,000 |  |
Net investment income earned | $ 4,500,000 | $ 2,300,000 | $ 24,000,000 | $ 11,100,000 |

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