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Investments - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Investment [Line Items] |  |  |
Cash recoveries |  | $ 995,000 |
Securities fair value | $ 5,974 | 5,872 |
Fair value of securities held by bankruptcy remote trust | 346,212 | 360,759 |
Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | 431,630 | 450,307 |
Unrealized losses on securities | 86,480 | 29,944 |
Other investments | 23,179 | 32,318 | $ 16,952
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 108,043 | 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 | 1,855,694 | 890,952 |
Gross unrealized loss | 100,503 | 53,273 |
Ambac Wrapped Securities [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 30,482 |  |
Gains (losses) on securities held as of reporting date [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other investments | 13,388 | 20,180 | $ 7,649
Real Estate [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | 33,154 | 33,303 |
Hedge Funds, Multi-strategy [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | 53,054 | 53,985 |
Interest Rate Contract [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | 136,603 | 261,315 |
Illiquid Investments [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | 67,787 | 39,068 |
Insurance Linked [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | 22,666 | 0 |
Equity [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | 53,675 | 32,633 |
Equity investments in pooled funds [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | 366,939 | 420,304 |
Reported Value Measurement [Member] | Interest Rate Contract [Member] | Successor [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments | $ 2,823 | $ 51,158 |

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