Derivative Instruments - Summary of Gross Principal Notional Outstanding for CDS Contracts (Detail) - Other Derivatives [Member] - Successor [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Ambac Rating
Notional outstanding	$ 325,890	$ 737,380
AAA Rating [Member]
Ambac Rating
Notional outstanding	0	0
AA Rating [Member]
Ambac Rating
Notional outstanding	175,765	315,201
A Rating [Member]
Ambac Rating
Notional outstanding	0	227,146
BBB Rating [Member]
Ambac Rating
Notional outstanding	150,125	127,250
Below Investment Grade Rating [Member]
Ambac Rating
Notional outstanding	$ 0	$ 67,783