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	Mar. 31, 2018	Dec. 31, 2017
Investments:
Fixed income securities	$ 4,277,297	$ 5,309,161
Variable Interest Entities [Member]
Investments:
Fixed income securities	2,955,763	2,914,145
Corporate Obligations [Member]
Investments:
Fixed income securities	$ 2,955,763	$ 2,914,145