Summary of Estimated Fair Values of Bonds Held on Deposit (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		$ 559,069	$ 582,431
On Deposit With Governmental Authorities
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		29,079	38,815
Intercompany Trusts Held For Benefit Of U.S. Policyholders
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		351,002	375,827
Held In Trust Pursuant To Third Party Requirements
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		88,178	66,544
Letter Of Credit Held For Third Party Requirements
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		4,871	5,598
Securities held as collateral for borrowing arrangements
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	[1]	$ 85,939	$ 95,647

[1] Amount required to collateralize margin borrowing facilities.