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Derivative Instruments - Summarize Information by Major Category of CDS Contracts (Detail) (USD $) In Thousands, unless otherwise specified | 9 Months Ended | 12 Months Ended
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Sep. 30, 2012 Transactions | Dec. 31, 2011 Transactions
Summary of information by major category of CDS contracts |  |
Number of CDS transactions | 57 | 68
Remaining expected weighted-average life of obligations (in years) | 3 years 6 months | 4 years 1 month 6 days
Gross principal notional outstanding | $ 12,274,885 | $ 14,166,612
Net derivative liabilities at fair value | (52,535) |
Credit Derivatives [Member] |  |
Summary of information by major category of CDS contracts |  |
Net derivative liabilities at fair value | (187,121) | (190,653)
CLOs [Member] |  |
Summary of information by major category of CDS contracts |  |
Number of CDS transactions | 35 | 44
Remaining expected weighted-average life of obligations (in years) | 2 years 1 month 6 days | 2 years 8 months 12 days
Gross principal notional outstanding | 7,067,409 | 8,228,577
CLOs [Member] | Credit Derivatives [Member] |  |
Summary of information by major category of CDS contracts |  |
Net derivative liabilities at fair value | (38,182) | (54,320)
Other [Member] |  |
Summary of information by major category of CDS contracts |  |
Number of CDS transactions | 22 | 24
Remaining expected weighted-average life of obligations (in years) | 5 years 6 months | 6 years
Gross principal notional outstanding | 5,207,476 | 5,938,035
Other [Member] | Credit Derivatives [Member] |  |
Summary of information by major category of CDS contracts |  |
Net derivative liabilities at fair value | $ (148,939) | $ (136,333)

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- Definition Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Fair value of the gross liabilities less the gross assets of a derivative liability or group of derivative liabilities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611 + Details
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- Definition The number of derivative instruments of a particular group held by the entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5580258-113959 + Details
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- Definition Aggregate notional amount of credit risk derivatives. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Notional Amount -URI http://asc.fasb.org/extlink&oid=6519104 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5580258-113959 + Details
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