Business Segments - Segment Premium Income by Distribution Channel and Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of segments | segment									4
Segment Reporting Information [Line Items]
Amount	$ 968,551	$ 961,817	$ 953,702	$ 929,835	$ 906,684	$ 899,993	$ 897,484	$ 890,973	$ 3,813,905	$ 3,595,134	$ 3,421,906
% of Total									100.00%	100.00%	100.00%
Life
Segment Reporting Information [Line Items]
Amount									$ 2,672,804	$ 2,517,784	$ 2,406,555
% of Total									100.00%	100.00%	100.00%
Health
Segment Reporting Information [Line Items]
Amount									$ 1,141,097	$ 1,077,346	$ 1,015,339
% of Total									100.00%	100.00%	100.00%
Annuity
Segment Reporting Information [Line Items]
Amount									$ 4	$ 4	$ 12
% of Total									100.00%	100.00%	100.00%
American Income
Segment Reporting Information [Line Items]
Amount									$ 1,363,460	$ 1,259,942	$ 1,174,646
% of Total									36.00%	35.00%	34.00%
American Income | Life
Segment Reporting Information [Line Items]
Amount									$ 1,257,726	$ 1,160,495	$ 1,081,333
% of Total									47.00%	46.00%	45.00%
American Income | Health
Segment Reporting Information [Line Items]
Amount									$ 105,734	$ 99,447	$ 93,313
% of Total									9.00%	9.00%	9.00%
American Income | Annuity
Segment Reporting Information [Line Items]
Amount									$ 0	$ 0	$ 0
% of Total									0.00%	0.00%	0.00%
Direct to Consumer
Segment Reporting Information [Line Items]
Amount									$ 983,486	$ 933,100	$ 905,232
% of Total									26.00%	26.00%	26.00%
Direct to Consumer | Life
Segment Reporting Information [Line Items]
Amount									$ 906,959	$ 855,543	$ 828,935
% of Total									34.00%	34.00%	34.00%
Direct to Consumer | Health
Segment Reporting Information [Line Items]
Amount									$ 76,527	$ 77,557	$ 76,297
% of Total									7.00%	7.00%	7.00%
Direct to Consumer | Annuity
Segment Reporting Information [Line Items]
Amount									$ 0	$ 0	$ 0
% of Total									0.00%	0.00%	0.00%
Liberty National
Segment Reporting Information [Line Items]
Amount									$ 482,732	$ 475,129	$ 470,256
% of Total									13.00%	13.00%	14.00%
Liberty National | Life
Segment Reporting Information [Line Items]
Amount									$ 293,897	$ 285,551	$ 278,878
% of Total									11.00%	11.00%	12.00%
Liberty National | Health
Segment Reporting Information [Line Items]
Amount									$ 188,835	$ 189,578	$ 191,378
% of Total									16.00%	18.00%	19.00%
Liberty National | Annuity
Segment Reporting Information [Line Items]
Amount									$ 0	$ 0	$ 0
% of Total									0.00%	0.00%	0.00%
United American
Segment Reporting Information [Line Items]
Amount									$ 462,672	$ 427,157	$ 392,539
% of Total									12.00%	12.00%	12.00%
United American | Life
Segment Reporting Information [Line Items]
Amount									$ 9,688	$ 10,571	$ 11,451
% of Total									0.00%	1.00%	1.00%
United American | Health
Segment Reporting Information [Line Items]
Amount									$ 452,980	$ 416,582	$ 381,076
% of Total									40.00%	39.00%	38.00%
United American | Annuity
Segment Reporting Information [Line Items]
Amount									$ 4	$ 4	$ 12
% of Total									100.00%	100.00%	100.00%
Family Heritage
Segment Reporting Information [Line Items]
Amount									$ 321,274	$ 298,012	$ 276,776
% of Total									8.00%	8.00%	8.00%
Family Heritage | Life
Segment Reporting Information [Line Items]
Amount									$ 4,253	$ 3,830	$ 3,501
% of Total									0.00%	0.00%	0.00%
Family Heritage | Health
Segment Reporting Information [Line Items]
Amount									$ 317,021	$ 294,182	$ 273,275
% of Total									28.00%	27.00%	27.00%
Family Heritage | Annuity
Segment Reporting Information [Line Items]
Amount									$ 0	$ 0	$ 0
% of Total									0.00%	0.00%	0.00%
Other
Segment Reporting Information [Line Items]
Amount									$ 200,281	$ 201,794	$ 202,457
% of Total									5.00%	6.00%	6.00%
Other | Life
Segment Reporting Information [Line Items]
Amount									$ 200,281	$ 201,794	$ 202,457
% of Total									8.00%	8.00%	8.00%
Other | Health
Segment Reporting Information [Line Items]
Amount									$ 0	$ 0	$ 0
% of Total									0.00%	0.00%	0.00%
Other | Annuity
Segment Reporting Information [Line Items]
Amount									$ 0	$ 0	$ 0
% of Total									0.00%	0.00%	0.00%