Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Parenthetical) (Detail) (Ambac UK [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Ambac UK [Member]
Investment [Line Items]
Asset-backed securities fair value	$ 51,395	$ 50,953