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 Ambac [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investments:
Fixed income securities	$ 6,771,159	$ 6,282,658
Variable Interest Entities [Member]
Investments:
Fixed income securities	2,651,683	2,475,182
Corporate Debt Securities [Member]
Investments:
Fixed income securities	$ 2,651,683	$ 2,475,182