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Investments - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017
Investment [Line Items] |  |  |  |  |
Securities fair value | $ 5,912 |  | $ 5,912 |  | $ 5,974
Fair Value of Securities Placed in Trust | 0 |  | 0 |  | 346,212
Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Other investments | 394,396 |  | 394,396 |  | 431,630
Unrealized losses on securities | 17,304 |  | 17,304 |  | 86,480
Other investments | 4,920 | $ 4,217 | 4,609 | $ 12,626 |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 34,773 |  | 34,773 |  | 108,043
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 | 176,712 |  | 176,712 |  | 1,855,694
Gross unrealized loss | 12,293 |  | 12,293 |  | 100,503
Gains (losses) on securities held as of reporting date [Member] | Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Other investments | 3,288 | $ 930 | 728 | $ 6,513 |
Ambac Assurance [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Unsettled Amounts Secured Notes from LSNI | 50,878 |  | 50,878 |  |
Ambac UK [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Asset Backed Securities Fair Value Disclosure | 172,531 |  | 172,531 |  | 170,280
Interest Rate Contract [Member] | Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Other investments | 145,981 |  | 145,981 |  | 136,603
Reported Value Measurement [Member] | Interest Rate Contract [Member] | Successor [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Other investments | $ 2,866 |  | $ 2,866 |  | $ 2,823

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