Schedule IV. Reinsurance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Life insurance in force, gross amount	$ 191,249,516	$ 185,212,195	$ 179,902,605
Life insurance in force, ceded to other companies	676,988	688,384	705,152
Life insurance in force, assumed from other companies	2,774,388	3,019,737	3,211,423
Life insurance in force, net amount	$ 193,346,916	$ 187,543,548	$ 182,408,876
Life insurance in force, percentage of amount assumed to net	1.40%	1.60%	1.80%
Premium, gross amount	$ 3,566,996	$ 3,392,430	$ 3,252,120
Premium, ceded to other companies	7,880	8,249	8,146
Premium, assumed from other companies	20,384	21,305	21,912
Premium, net amount	$ 3,579,500	$ 3,405,486	$ 3,265,886
Percentage of amount assumed to net	0.60%	0.60%	0.70%
Policy charges	$ 15,600	$ 16,400	$ 17,000
Life insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Premium, gross amount	2,486,127	2,373,423	2,272,038
Premium, ceded to other companies	4,357	4,581	4,437
Premium, assumed from other companies	20,384	21,305	21,912
Premium, net amount	$ 2,502,154	$ 2,390,147	$ 2,289,513
Percentage of amount assumed to net	0.80%	0.90%	1.00%
Health insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Premium, gross amount	$ 1,080,869	$ 1,019,007	$ 980,082
Premium, ceded to other companies	3,523	3,668	3,709
Premium, assumed from other companies	0	0	0
Premium, net amount	$ 1,077,346	$ 1,015,339	$ 976,373
Percentage of amount assumed to net	0.00%	0.00%	0.00%