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Fair Value Measurements - Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011
Realized gains or (losses) and other settlements on credit derivative contracts [Member] |  |
Total gains or losses included in earnings for the period | $ 13,713 | $ 17,001
Unrealized gains or (losses) on credit derivative contracts [Member] |  |
Total gains or losses included in earnings for the period | (22,932) | 31,031
Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date | (35,331) | 9,625
Interest rate swaps [Member] |  |
Total gains or losses included in earnings for the period | (70,415) | (389,720)
Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date | (78,505) | (356,354)
Variable interest entity [Member] |  |
Total gains or losses included in earnings for the period | 702,496 | 854,106
Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date | 702,977 | 854,091
Other income [Member] |  |
Total gains or losses included in earnings for the period | 98,488 | 4,925
Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date | (2,222) | 4,925
Net investment income [Member] |  |
Total gains or losses included in earnings for the period | $ (3) | $ (3,467)

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- Definition The amount of gains or losses included in earnings attributable to unrealized gains or losses on financial instruments measured on a recurring basis using unobservable inputs that are still held at the reporting date. + References No definition available. + Details
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- Definition This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets); the fair value of which assets and liabilities was or is measured on a recurring basis using significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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- Definition This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets) in investment income; the fair value of which assets was or is measured on a recurring basis using significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 157 -Paragraph 32 -Subparagraph c(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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