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Summary of Estimated Fair Values of Bonds Held on Deposit (Detail) - USD ($) $ in Thousands | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | $ 256,952 | $ 431,356
On Deposit With Governmental Authorities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 27,082 | 26,431
Intercompany Trusts Held For Benefit Of U.S. Policyholders |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 142,496 | 179,116
Held In Trust Pursuant To Third Party Requirements |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 84,174 | 133,122
Letter Of Credit Held For Third Party Requirements |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 2,645 | 1,458
Securities Held As Collateral |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | $ 555 | $ 91,229

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