Schedule IV. Reinsurance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Life insurance in force, gross amount	$ 203,894,460	$ 191,249,516	$ 185,212,195
Life insurance in force, ceded to other companies	669,063	676,988	688,384
Life insurance in force, assumed from other companies	2,551,770	2,774,388	3,019,737
Life insurance in force, net amount	$ 205,777,167	$ 193,346,916	$ 187,543,548
Life insurance in force, percentage of amount assumed to net	1.20%	1.40%	1.60%
Premium, gross amount	$ 3,787,025	$ 3,566,996	$ 3,392,430
Premium, ceded to other companies	7,614	7,880	8,249
Premium, assumed from other companies	19,775	20,384	21,305
Premium, net amount	$ 3,799,186	$ 3,579,500	$ 3,405,486
Percentage of amount assumed to net	0.50%	0.60%	0.60%
Policy charges	$ 14,700	$ 15,600	$ 16,400
Life insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Premium, gross amount	2,642,555	2,486,127	2,373,423
Premium, ceded to other companies	4,241	4,357	4,581
Premium, assumed from other companies	19,775	20,384	21,305
Premium, net amount	$ 2,658,089	$ 2,502,154	$ 2,390,147
Percentage of amount assumed to net	0.70%	0.80%	0.90%
Health insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Premium, gross amount	$ 1,144,470	$ 1,080,869	$ 1,019,007
Premium, ceded to other companies	3,373	3,523	3,668
Premium, assumed from other companies	0	0	0
Premium, net amount	$ 1,141,097	$ 1,077,346	$ 1,015,339
Percentage of amount assumed to net	0.00%	0.00%	0.00%