Summary of Estimated Fair Values of Bonds Held on Deposit (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 434,042	$ 418,831
On Deposit With Governmental Authorities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	26,500	25,855
Intercompany Trusts Held For Benefit Of U.S. Policyholders
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	192,269	209,028
Held In Trust Pursuant To Third Party Requirements
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	123,811	98,417
Letter Of Credit Held For Third Party Requirements
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,458	2,317
Securities Held As Collateral
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 90,004	$ 83,214