Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Phantom) (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Ambac UK [Member]
Investment [Line Items]
Asset Backed Securities Fair Value Disclosure	$ 118,968	$ 119,802