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Derivative Instruments - Summarize Information by Major Category of CDS Contracts (Detail) (USD $) In Thousands, unless otherwise specified |  |  | 12 Months Ended |  | 6 Months Ended |  | 12 Months Ended |  | 6 Months Ended |  | 12 Months Ended |  | 6 Months Ended |
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Jun. 30, 2013 | Dec. 31, 2012 | Dec. 31, 2012 Predecessor Ambac [Member] Transactions | Dec. 31, 2012 Predecessor Ambac [Member] Credit Derivatives [Member] | Jun. 30, 2013 Successor Ambac [Member] Transactions | Jun. 30, 2013 Successor Ambac [Member] Credit Derivatives [Member] | Dec. 31, 2012 CLO [Member] Predecessor Ambac [Member] Transactions | Dec. 31, 2012 CLO [Member] Predecessor Ambac [Member] Credit Derivatives [Member] | Jun. 30, 2013 CLO [Member] Successor Ambac [Member] Transactions | Jun. 30, 2013 CLO [Member] Successor Ambac [Member] Credit Derivatives [Member] | Dec. 31, 2012 Other [Member] Predecessor Ambac [Member] Transactions | Dec. 31, 2012 Other [Member] Predecessor Ambac [Member] Credit Derivatives [Member] | Jun. 30, 2013 Other [Member] Successor Ambac [Member] Transactions | Jun. 30, 2013 Other [Member] Successor Ambac [Member] Credit Derivatives [Member]
Summary of information by major category of CDS contracts |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of CDS transactions |  |  | 51 |  | 29 |  | 30 |  | 9 |  | 21 |  | 20 |
Remaining expected weighted-average life of obligations (in years) |  |  | 3 years 7 months 6 days |  | 4 years 3 months 18 days |  | 2 years 2 months 12 days |  | 2 years 6 months |  | 5 years 2 months 12 days |  | 5 years 1 month 6 days |
Gross principal notional outstanding | $ 5,861,060 | $ 11,281,777 | $ 11,281,777 |  | $ 5,861,060 |  | $ 6,155,767 |  | $ 1,750,217 |  | $ 5,126,010 |  | $ 4,110,843 |
Net derivative liabilities at fair value |  |  |  | $ (213,585) |  | $ (232,267) |  | $ (34,645) |  | $ (11,996) |  | $ (178,940) |  | $ (220,271)

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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 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611 Reference 2: 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 3: 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 Reference 4: 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 + 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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