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Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2014 | Dec. 31, 2013
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Residential Mortgage-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Gross Unrealized Loss | $ 20,408 |
Other Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Gross Unrealized Loss | 24,618 |
Successor Ambac [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 2,333,756 | 2,920,966
Less than 12 Months, Gross Unrealized Loss | 83,446 | 116,634
Successor Ambac [Member] | Short-Term [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 1,702 | 0
Less than 12 Months, Gross Unrealized Loss | 0 | 0
Successor Ambac [Member] | Fixed Income Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 2,332,054 | 2,920,966
Less than 12 Months, Gross Unrealized Loss | 83,446 | 116,634
Successor Ambac [Member] | Fixed Income Securities [Member] | Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 415,721 | 437,683
Less than 12 Months, Gross Unrealized Loss | 16,978 | 28,427
Successor Ambac [Member] | Fixed Income Securities [Member] | Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 738,842 | 877,356
Less than 12 Months, Gross Unrealized Loss | 14,253 | 23,894
Successor Ambac [Member] | Fixed Income Securities [Member] | Foreign Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 104,908 | 117,905
Less than 12 Months, Gross Unrealized Loss | 4,818 | 6,901
Successor Ambac [Member] | Fixed Income Securities [Member] | U.S. Government Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 29,753 | 70,044
Less than 12 Months, Gross Unrealized Loss | 1,663 | 2,176
Successor Ambac [Member] | Fixed Income Securities [Member] | U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 31,619 | 5,834
Less than 12 Months, Gross Unrealized Loss | 65 | 70
Successor Ambac [Member] | Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 441,506 | 644,502
Less than 12 Months, Gross Unrealized Loss | 20,408 | 18,105
Successor Ambac [Member] | Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 128,956 | 137,685
Less than 12 Months, Gross Unrealized Loss | 643 | 463
Successor Ambac [Member] | Fixed Income Securities [Member] | Other Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 440,749 | 629,957
Less than 12 Months, Gross Unrealized Loss | $ 24,618 | $ 36,598

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- Definition Amount of accumulated pre-tax unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months impacting investments. + References No definition available. + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
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