Derivative Instruments - Summary of Gross Principal Notional Outstanding for CDS Contracts (Detail) - Successor [Member] - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Ambac Rating
Notional outstanding	$ 397,003	$ 737,380
Other Derivatives [Member]
Ambac Rating
Notional outstanding	397,003	737,380
Other Derivatives [Member] | AAA Rating [Member]
Ambac Rating
Notional outstanding	0	0
Other Derivatives [Member] | AA Rating [Member]
Ambac Rating
Notional outstanding	175,576	315,201
Other Derivatives [Member] | A Rating [Member]
Ambac Rating
Notional outstanding	0	227,146
Other Derivatives [Member] | BBB Rating [Member]
Ambac Rating
Notional outstanding	147,712	127,250
Other Derivatives [Member] | Below Investment Grade Rating [Member]
Ambac Rating
Notional outstanding	$ 73,715	$ 67,783