Business Segments - Other Balances by Segment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Other Significant Reconciling Item [Line Items]
Future policy benefits	$ 13,439,472	$ 12,825,837
Unearned and advance premiums	61,430	64,017
Policy claims and other benefits payable	333,294	299,565
Debt	1,460,268	1,397,640
Other	1,949,100	2,282,167
Total	17,243,564	16,869,226
Life
Segment Reporting, Other Significant Reconciling Item [Line Items]
Future policy benefits	10,353,286	9,825,776
Unearned and advance premiums	16,927	16,828
Policy claims and other benefits payable	186,429	156,437
Total	10,556,642	9,999,041
Health
Segment Reporting, Other Significant Reconciling Item [Line Items]
Future policy benefits	1,831,338	1,706,870
Unearned and advance premiums	44,503	47,189
Policy claims and other benefits payable	146,865	143,128
Total	2,022,706	1,897,187
Annuity
Segment Reporting, Other Significant Reconciling Item [Line Items]
Future policy benefits	1,254,848	1,293,191
Total	1,254,848	1,293,191
Investment
Segment Reporting, Other Significant Reconciling Item [Line Items]
Debt	1,460,268	1,397,640
Total	1,460,268	1,397,640
Other
Segment Reporting, Other Significant Reconciling Item [Line Items]
Other	1,949,100	2,282,167
Total	$ 1,949,100	$ 2,282,167