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Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) - Successor [Member] - USD ($) $ in Thousands | Mar. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | $ 1,439,509 | $ 2,281,230
Less than 12 Months, Gross Unrealized Loss | 46,348 | 82,799
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 568,791 | 463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 30,483 | 21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 2,008,300 | 2,744,550
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 76,831 | 104,206
Short-Term [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 1,983 | 9,982
Less than 12 Months, Gross Unrealized Loss | 0 | 1
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 0 | 0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 0 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 1,983 | 9,982
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 0 | 1
Fixed Income Investments And Other Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 1,439,509 | 2,216,675
Less than 12 Months, Gross Unrealized Loss | 46,348 | 82,742
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 568,791 | 463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 30,483 | 21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 2,008,300 | 2,679,995
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 76,831 | 104,149
Fixed Income Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 1,437,526 | 2,206,693
Less than 12 Months, Gross Unrealized Loss | 46,348 | 82,741
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 568,791 | 463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 30,483 | 21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 2,006,317 | 2,670,013
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 76,831 | 104,148
Fixed Income Securities [Member] | Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 58,996 | 117,008
Less than 12 Months, Gross Unrealized Loss | 1,587 | 2,070
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 76,741 | 114,708
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 3,382 | 6,118
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 135,737 | 231,716
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 4,969 | 8,188
Fixed Income Securities [Member] | Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 266,795 | 938,916
Less than 12 Months, Gross Unrealized Loss | 5,198 | 21,331
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 137,811 | 92,581
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 2,703 | 3,001
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 404,606 | 1,031,497
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 7,901 | 24,332
Fixed Income Securities [Member] | Foreign Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 1,838 | 34,904
Less than 12 Months, Gross Unrealized Loss | 17 | 1,018
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 1,556 | 8,584
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 44 | 805
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 3,394 | 43,488
Fixed Income Securities [Member] | U.S. Government Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 7,903 | 2,938
Less than 12 Months, Gross Unrealized Loss | 73 | 18
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 8,436 | 10,658
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 20 | 170
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 16,339 | 13,596
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 93 | 188
Fixed Income Securities [Member] | U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 0 | 0
Less than 12 Months, Gross Unrealized Loss | 0 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 4,186 | 4,212
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 9 | 27
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 4,186 | 4,212
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 9 | 27
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 624,811 | 584,699
Less than 12 Months, Gross Unrealized Loss | 35,383 | 53,367
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 304,949 | 213,303
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 24,168 | 11,250
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 929,760 | 798,002
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 59,551 | 64,617
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 67,563 | 77,538
Less than 12 Months, Gross Unrealized Loss | 1,550 | 1,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 19,767 | 0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 117 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 87,330 | 77,538
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 1,667 | 1,481
Fixed Income Securities [Member] | Other Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 409,620 | 450,690
Less than 12 Months, Gross Unrealized Loss | 2,540 | 3,456
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 15,345 | 19,274
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 40 | 36
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 424,965 | 469,964
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 2,580 | 3,492
Fixed Income Securities [Member] | Foreign Government Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 61 | 1,823
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 0 | 64,555
Less than 12 Months, Gross Unrealized Loss | 0 | 57
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 0 | 0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 0 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 0 | 64,555
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 0 | 57
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member] | U.S. Government Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 0 | 64,555
Less than 12 Months, Gross Unrealized Loss | 0 | 57
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments | 0 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 0 | 64,555
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 0 | $ 57
Securities Pledged as Collateral [Member] | Securities Pledged as Collateral [Member] | U.S. Government Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | $ 0 |

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- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 Reference 2: 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 + Details
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