Selected Balance Sheet Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Supplemental Balance Sheet Information [Line Items]
Total Assets	$ 8,621,825	$ 8,670,275
Total Policyholder Liabilities	1,491,236	1,621,077
Annuity
Supplemental Balance Sheet Information [Line Items]
Total Assets	5,975,236	6,044,874
Total Policyholder Liabilities	484,398	567,814
Life Insurance
Supplemental Balance Sheet Information [Line Items]
Total Assets	2,646,589	2,625,401
Total Policyholder Liabilities	$ 1,006,838	$ 1,053,263