Special Purpose Entities, Including Variable Interest Entities - Summary of Fair Value of Fixed Income Securities, by Asset-Type, Held by Consolidated Variable Interest Entities (Detail) - Successor [Member] - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investments:
Fixed income securities	$ 5,794,058	$ 6,049,908
Variable Interest Entities [Member]
Investments:
Fixed income securities	2,785,608	2,622,566
Corporate Obligations [Member]
Investments:
Fixed income securities	$ 2,785,608	$ 2,622,566