Income Taxes - Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Fixed maturity investments	$ 8,692	$ 15,004
Carryover of tax losses	4,760	3,906
Total gross deferred tax assets	13,452	18,910
Deferred tax liabilities:
Unrealized gains	380,251	315,509
Employee and agent compensation	65,576	92,131
Deferred acquisition costs	618,889	975,873
Future policy benefits, unearned and advance premiums, and policy claims	248,752	391,451
Other liabilities	11,289	3,987
Total gross deferred tax liabilities	1,324,757	1,778,951
Net deferred tax liability	$ 1,311,305	$ 1,760,041