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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, 2019	Dec. 31, 2018
Ambac UK [Member]
Investment [Line Items]
Corporate and Asset Backed Securities Fair Value Disclosure	$ 144,530	$ 144,672

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- Definition

Corporate and Asset Backed Securities Fair Value Disclosure

+ References

No definition available.

+ Details

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- Definition

Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

+ Details

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- Details

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