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Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) - USD ($) $ in Thousands | Mar. 31, 2017 | Dec. 31, 2016
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Ambac Wrapped Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | $ 36,995 |
Successor [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 1,477,139 | $ 1,491,493
Less than 12 Months, Gross Unrealized Loss | 22,796 | 29,944
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 639,343 | 788,764
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 45,769 | 49,698
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 2,116,482 | 2,280,257
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 68,565 | 79,642
Successor [Member] | Below Investment Grade Securities and Non-Rated Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Below Investment Grade Securities And Non Rated Securities Continuous Unrealized Loss Position Fair Value | 985,032 | 890,952
Below Investment Grade Securities And Non Rated Securities Continuous Unrealized Loss Position Aggregate Losses | 48,888 | 53,273
Successor [Member] | Short-Term [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 126,441 | 65,176
Less than 12 Months, Gross Unrealized Loss | 109 | 44
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, Accumulated Loss | 0 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 126,441 | 65,176
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 109 | 44
Fixed Income Investments And Other Investments [Member] | Successor [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 68,565 | 79,642
Fixed Income Securities [Member] | Successor [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 1,350,698 | 1,426,317
Less than 12 Months, Gross Unrealized Loss | 22,687 | 29,900
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 639,343 | 788,764
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 45,769 | 49,698
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 1,990,041 | 2,215,081
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 68,456 | 79,598
Fixed Income Securities [Member] | Successor [Member] | Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 140,215 | 98,147
Less than 12 Months, Gross Unrealized Loss | 2,633 | 2,045
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 109,137 | 122,928
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 4,951 | 5,160
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 249,352 | 221,075
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 7,584 | 7,205
Fixed Income Securities [Member] | Successor [Member] | Corporate Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 756,173 | 963,513
Less than 12 Months, Gross Unrealized Loss | 15,149 | 20,232
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 3,937 | 6,492
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 154 | 328
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 760,110 | 970,005
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 15,303 | 20,560
Fixed Income Securities [Member] | Successor [Member] | U.S. Government Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 10,615 | 6,037
Less than 12 Months, Gross Unrealized Loss | 103 | 93
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 5,021 | 5,045
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 4 | 4
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 15,636 | 11,082
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 107 | 97
Fixed Income Securities [Member] | Successor [Member] | U.S. Agency Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 4,018 | 4,060
Less than 12 Months, Gross Unrealized Loss | 2 | 3
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, Accumulated Loss | 0 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 4,018 | 4,060
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 2 | 3
Fixed Income Securities [Member] | Successor [Member] | Residential Mortgage-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 280,529 | 226,889
Less than 12 Months, Gross Unrealized Loss | 4,081 | 7,201
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 442,162 | 550,807
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 33,178 | 36,584
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 722,691 | 777,696
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 37,259 | 43,785
Fixed Income Securities [Member] | Successor [Member] | Collateralized Debt Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 23,149 | 6,986
Less than 12 Months, Gross Unrealized Loss | 2 | 23
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 8,005 | 25,780
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 2 | 197
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 31,154 | 32,766
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 4 | 220
Fixed Income Securities [Member] | Successor [Member] | Other Asset-Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 132,395 | 115,622
Less than 12 Months, Gross Unrealized Loss | 685 | 203
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 71,081 | 77,712
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 7,480 | 7,425
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 203,476 | 193,334
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 8,165 | 7,628
Fixed Income Securities [Member] | Successor [Member] | Foreign Government Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 3,604 | 5,063
Less than 12 Months, Gross Unrealized Loss | 32 | 100
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, Accumulated Loss | 0 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value | 3,604 | 5,063
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 32 | 100
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member] | Successor [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 0 | 0
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member] | Successor [Member] | U.S. Government Obligations [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | $ 0 | $ 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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