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Investments - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 | Mar. 31, 2016 | Dec. 31, 2016
Investment [Line Items] |  |  |
Securities fair value | $ 5,859 |  | $ 5,872
Fair Value of Securities Placed in Trust | 355,223 |  | 360,759
Successor [Member] |  |  |
Investment [Line Items] |  |  |
Unrealized losses on securities | 22,796 |  | 29,944
Cash recoveries |  |  | 995,000
Other investments | 8,409 | $ 2,839 |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 68,565 |  | 79,642
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 | 985,032 |  | 890,952
Gross unrealized loss | 48,888 |  | 53,273
Ambac Wrapped Securities [Member] |  |  |
Investment [Line Items] |  |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 36,995 |  |
Gains (losses) on securities held as of reporting date [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other investments | 5,928 | $ 1,301 |
Ambac UK [Member] |  |  |
Investment [Line Items] |  |  |
Asset Backed Securities Fair Value Disclosure | $ 166,126 |  | $ 118,813

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