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Background and Business Description - Additional Information (Detail) | 3 Months Ended | 4 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2017 USD ($) $ / shares shares | Mar. 31, 2017 USD ($) | Jun. 30, 2016 USD ($) | Apr. 30, 2013 shares | Jun. 30, 2017 USD ($) $ / shares shares | Jun. 30, 2016 USD ($) | Dec. 31, 2016 USD ($) $ / shares shares | May 01, 2013 $ / shares shares
Background And Basis Of Presentation [Line Items] |  |  |  |  |  |  |  |
Gain (Loss) on Sale of Derivatives | $ 43,443,000 |  |  |  | $ 42,157,000 |  |  |
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount | 2,600,000 |  |  |  |  |  |  |
Entity Incorporation, Date of Incorporation |  |  |  |  | Apr. 29, 1991 |  |  |
Investment Warrants Expiration Date |  |  |  | Apr. 30, 2023 |  |  |  |
Possible Increase in Loss Reserves Related to Puerto Rico |  |  |  |  | $ 0 |  |  |
Payments for Derivative Instrument, Financing Activities |  |  |  |  | 103,592,000 |  |  |
Ambac Assurance [Member] |  |  |  |  |  |  |  |
Background And Basis Of Presentation [Line Items] |  |  |  |  |  |  |  |
Net par exposure for policies allocated to the Segregated Account | 10,772,572,000 |  |  |  | 10,772,572,000 |  |  |
Minimum surplus amount | 100,000,000 |  |  |  | 100,000,000 |  |  |
Successor [Member] |  |  |  |  |  |  |  |
Background And Basis Of Presentation [Line Items] |  |  |  |  |  |  |  |
Gain (Loss) on Sale of Derivatives | 1,134,000 |  | $ 233,000 |  | 1,333,000 | $ 485,000 |  |
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount | $ 13,190,000 |  | $ 5,081,000 |  | $ 29,470,000 | $ 20,057,000 |  |
Number of Reportable Segments |  | 2 |  |  |  |  |  |
Common stock, shares authorized | shares | 130,000,000 |  |  |  | 130,000,000 |  | 130,000,000 |
Common Stock, Par or Stated Value Per Share | $ / shares | $ 0.01 |  |  |  | $ 0.01 |  | $ 0.01 | $ 0.01
Preferred stock, shares authorized | shares | 20,000,000 |  |  |  | 20,000,000 |  | 20,000,000 |
Preferred Stock, Par or Stated Value Per Share | $ / shares | $ 0.01 |  |  |  | $ 0.01 |  | $ 0.01 |
Common stock, shares issued | shares | 45,275,982 |  |  |  | 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 |  |  |  |  | $ 221,604,000 |  |  |
Derivative Liability | $ 91,549,000 |  |  |  | 91,549,000 |  | $ 319,286,000 |
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 |  |  |
Previous Benefit Through Reduction of Loss and LAE |  |  |  |  | 53,000,000 |  |  |
Total Benefit Related to Ballantyne Settlement |  |  |  |  | 144,600,000 |  |  |
Derivative Liability Termination Payment [Domain] |  |  |  |  |  |  |  |
Background And Basis Of Presentation [Line Items] |  |  |  |  |  |  |  |
Payments for Derivative Instrument, Financing Activities |  |  |  |  | $ 94,407,000 |  |  |
Derivative Financial Instruments, Liabilities [Member] |  |  |  |  |  |  |  |
Background And Basis Of Presentation [Line Items] |  |  |  |  |  |  |  |
Derivative Liability |  | $ 147,035,000 |  |  |  |  |  |

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