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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