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Investments - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015 | 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 | $ 5,914 |  | $ 5,914 |  | $ 6,762
Fair Value of Securities Placed in Trust | 369,127 |  | 369,127 |  | 396,100
Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Unrealized losses on securities | 13,911 |  | 13,911 |  | 82,799
Other investments | 11,387 | $ (1,424) | 20,616 | $ 10,702 |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 52,657 |  | 52,657 |  | 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 | 985,810 |  | 985,810 |  | 953,000
Gross unrealized loss | 46,373 |  | 46,373 |  | 69,214
Ambac Wrapped Securities [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 44,680 |  | 44,680 |  |
Gains (losses) on securities held as of reporting date [Member] | Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Other investments | 8,338 | $ (3,482) | 11,877 | $ (41) |
Ambac UK [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Asset Backed Securities Fair Value Disclosure | $ 120,028 |  | 120,028 |  | 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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- Definition Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 12 -Sentence Column A + Details
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