Derivative Instruments - Summary of Gross Principal Notional Outstanding for CDS Contracts (Detail) - Other Derivatives [Member] - Successor [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Ambac Rating
Notional outstanding	$ 311,237	$ 325,890
AAA Rating [Member]
Ambac Rating
Notional outstanding	0	0
AA Rating [Member]
Ambac Rating
Notional outstanding	165,387	175,765
A Rating [Member]
Ambac Rating
Notional outstanding	0	0
BBB Rating [Member]
Ambac Rating
Notional outstanding	145,850	150,125
Below Investment Grade Rating [Member]
Ambac Rating
Notional outstanding	$ 0	$ 0