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Investments - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2016 | Sep. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2015
Investment [Line Items] |  |  |  |  |
Payment of permitted policy claim (percent) |  |  |  | 25.00% |
Future payment of permitted policy claim (percent) |  |  |  | 45.00% |
Securities fair value | $ 5,939 |  |  |  | $ 6,762
Fair Value of Securities Placed in Trust | 381,249 |  |  |  | 396,100
Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Unrealized losses on securities | 46,348 |  |  |  | 82,799
Other investments | 2,839 |  | $ 9,651 |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 76,831 |  |  |  | 104,206
Below Investment Grade Securities and Non-Rated Securities [Member] | Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Fair value of below investment grade securities and non-rated securities | 1,053,711 |  |  |  | 953,000
Gross unrealized loss | 63,981 |  |  |  | 69,214
Ambac Wrapped Securities [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 57,269 |  |  |  |
Gains (losses) on securities held as of reporting date [Member] | Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Other investments | 1,301 |  | $ 6,255 |  |
Ambac UK [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Asset Backed Securities Fair Value Disclosure | $ 118,968 |  |  |  | $ 119,802
National Century Financial Enterprises, Inc. [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Cash recoveries |  | $ 0 |  | $ 35 |

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- Definition Percentage of the Segregated Account of Ambac Assurance's permitted policy claims that are to be paid in cash from July 2014 forward as approved by the Rehabilitation Court. + References No definition available. + Details
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- Definition Percentage of the Segregated Account of Ambac Assurance's permitted policy claims that were paid in cash from September 2012 through June 2014. + References No definition available. + Details
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