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Investments (Other Investment Portfolio by Strategy and the Remaining Commitment Amount Associated With Each Strategy) (Details) (USD $) | 3 Months Ended | 6 Months Ended |  | 6 Months Ended |  | 3 Months Ended | 6 Months Ended |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 Months Ended
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Jun. 30, 2012 | Jun. 30, 2011 | Jun. 30, 2012 | Jun. 30, 2011 | Dec. 31, 2011 | Jun. 30, 2012 Other Investments [Member] | Dec. 31, 2011 Other Investments [Member] | Mar. 31, 2012 Alternative Investments [Member] | Mar. 31, 2011 Alternative Investments [Member] | Mar. 31, 2012 Alternative Investments [Member] | Mar. 31, 2011 Alternative Investments [Member] | Jun. 30, 2012 Alternative Investments [Member] | Dec. 31, 2011 Alternative Investments [Member] | Jun. 30, 2012 Secondary Private Equity Member Alternative Investments [Member] | Dec. 31, 2011 Secondary Private Equity Member Alternative Investments [Member] | Jun. 30, 2012 Private Equity [Member] Alternative Investments [Member] | Dec. 31, 2011 Private Equity [Member] Alternative Investments [Member] | Jun. 30, 2012 Energy Power Generation [Member] Alternative Investments [Member] | Dec. 31, 2011 Energy Power Generation [Member] Alternative Investments [Member] | Jun. 30, 2012 Distressed Debt [Member] Alternative Investments [Member] | Dec. 31, 2011 Distressed Debt [Member] Alternative Investments [Member] | Jun. 30, 2012 Real Estate Strategy [Member] Alternative Investments [Member] | Dec. 31, 2011 Real Estate Strategy [Member] Alternative Investments [Member] | Jun. 30, 2012 Mezzanine Financing [Member] Alternative Investments [Member] | Dec. 31, 2011 Mezzanine Financing [Member] Alternative Investments [Member] | Jun. 30, 2012 Venture Capital [Member] Alternative Investments [Member] | Dec. 31, 2011 Venture Capital [Member] Alternative Investments [Member] | Jun. 30, 2012 Other Securities [Member] | Dec. 31, 2011 Other Securities [Member] | Jun. 30, 2012 Previously Existing Partnership Commitments [Member] | Jun. 30, 2012 New Mezzanine Limited Partnerships [Member]
Carrying Value | $ 125,540,000 |  | $ 125,540,000 |  | $ 128,301,000 | $ 125,540,000 | $ 128,301,000 |  |  |  |  | $ 121,578,000 | $ 124,548,000 | $ 29,596,000 | $ 30,114,000 | $ 23,739,000 | $ 21,736,000 | $ 21,578,000 | $ 25,913,000 | $ 14,702,000 | $ 16,953,000 | $ 12,961,000 | $ 13,767,000 | $ 11,146,000 | $ 8,817,000 | $ 7,856,000 | $ 7,248,000 | $ 3,962,000 | $ 3,753,000 |  |
Remaining Commitment |  |  |  |  |  | 62,206,000 |  |  |  |  |  | 60,712,000 |  | 8,651,000 |  | 3,984,000 |  | 10,383,000 |  | 2,986,000 |  | 10,473,000 |  | 23,435,000 |  | 800,000 |  | 1,494,000 |  |  | 8,200,000
Decrease in other investments |  |  | (2,800,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributions from alternative investments |  |  | 13,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net investment income earned | 34,006,000 | 39,345,000 | 66,634,000 | 82,818,000 |  | 5,000,000 |  | 3,000,000 | 7,900,000 | 5,000,000 | 19,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional contributions |  |  | $ 6,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,600,000 | $ 1,800,000

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- Definition This item represents the amount of funding that the company has provided on commitments in our other investment portfolio for the period. + References No definition available. + Details
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- Definition The income earned from investments in securities and other investments including dividends, interest, and returns on other investments. This item does not include realized gains (losses). + References No definition available. + Details
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- Definition Other investments not otherwise specified in the taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(f,g)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 12 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 7 -Section 03 -Paragraph 1 -Subparagraph g Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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