Investments - Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Fair Value Of Securities Deposited With Governmental Authorities	$ 7,613	$ 5,975
Fair Value of Securities Deposited in Connection wtih Letter of Credit	1,412
Market Value of Secured Note Collateral	205,960	209,983
Investment Portfolio [Member]
Investment [Line Items]
Fair Value of Cash and Securities Pledged to Derivative Counterparties	119,853	102,904
Ambac Assurance [Member]
Investment [Line Items]
Unsettled Amounts Secured Notes from LSNI	$ 0	$ 19,405

Fair value of cash and securities pledged to derivative counterparties.

No definition available.

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- Definition

Fair value of securities deposited with governmental authorities.

+ References

No definition available.

+ Details

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- Definition

Fair Value of Securities Deposited in Connection wtih Letter of Credit

+ References

No definition available.

+ Details

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- Definition

Market Value of Secured Note Collateral

+ References

No definition available.

+ Details

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- Definition

Unsettled Amounts Secured Notes from LSNI

+ 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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