Summary of Estimated Fair Values of Bonds Held on Deposit (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 131,664	$ 431,356
On Deposit With Governmental Authorities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	26,966	26,431
Intercompany Trusts Held For Benefit Of U.S. Policyholders
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0	179,116
Held In Trust Pursuant To Third Party Requirements
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	100,234	133,122
Letter Of Credit Held For Third Party Requirements
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	3,970	1,458
Securities Held As Collateral
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 494	$ 91,229