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Background and Business Description - Additional Information (Detail) | 3 Months Ended | 4 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2017 USD ($) Segment $ / shares shares | Apr. 30, 2013 shares | Dec. 31, 2016 $ / shares shares | May 01, 2013 $ / shares shares
Background And Basis Of Presentation [Line Items] |  |  |  |
Entity Incorporation, Date of Incorporation | Apr. 29, 1991 |  |  |
Number of reportable segments | Segment | 2 |  |  |
Investment Warrants Expiration Date |  | Apr. 30, 2023 |  |
Possible Increase in Loss Reserves Related to Puerto Rico | $ 1,600,000,000 |  |  |
Ambac Assurance [Member] |  |  |  |
Background And Basis Of Presentation [Line Items] |  |  |  |
Net par exposure for policies allocated to the Segregated Account | 11,274,275,000 |  |  |
Minimum surplus amount | $ 100,000,000 |  |  |
Successor [Member] |  |  |  |
Background And Basis Of Presentation [Line Items] |  |  |  |
Common stock, shares authorized | shares | 130,000,000 |  | 130,000,000 |
Common Stock, Par or Stated Value Per Share | $ / shares | $ 0.01 |  | $ 0.01 | $ 0.01
Preferred stock, shares authorized | shares | 20,000,000 |  | 20,000,000 |
Preferred Stock, Par or Stated Value Per Share | $ / shares | $ 0.01 |  | $ 0.01 |
Common stock, shares issued | shares | 45,275,982 |  | 45,194,954 | 45,000,000
Warrants Distributed In Bankruptcy | shares |  | 5,047,138 |  | 5,047,138
Warrants issued exercise price | $ / shares |  |  |  | $ 16.67
Puerto Rico Losses in Public Finance Sector | $ 169,400,000 |  |  |
Successor [Member] | Ambac UK [Member] |  |  |  |
Background And Basis Of Presentation [Line Items] |  |  |  |
Ballantyne Settlement with JPMIM | 325,600,000 |  |  |
Ambac UK Benefit Through Loss Reduction | 91,600,000 |  |  |
Change in Loss Assumptions | (18,300,000) |  |  |
Net Impact of Change in Reserves Related to Ballantyne Settlement | 73,300,000 |  |  |
Previous Benefit Through Reduction of Loss and LAE | 53,000,000 |  |  |
Total Benefit Related to Ballantyne Settlement | $ 144,600,000 |  |  |

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