Business Segments - Assets by Segment (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and invested assets	$ 22,547,498	$ 19,923,204
Accrued investment income	248,991	245,129
Deferred acquisition costs	4,595,444	4,341,941	$ 4,137,925	$ 3,958,063
Goodwill	441,591	441,591
Other assets	1,213,207	1,025,595
Total assets	29,046,731	25,977,460
Other
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and invested assets	0	0
Accrued investment income	0	0
Deferred acquisition costs	0	0
Goodwill	0	0
Other assets	1,213,207	1,025,595
Total assets	1,213,207	1,025,595
Life | Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and invested assets	0	0
Accrued investment income	0	0
Deferred acquisition costs	3,982,158	3,768,797
Goodwill	309,609	309,609
Other assets	0	0
Total assets	4,291,767	4,078,406
Health | Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and invested assets	0	0
Accrued investment income	0	0
Deferred acquisition costs	610,071	569,126
Goodwill	131,982	131,982
Other assets	0	0
Total assets	742,053	701,108
Annuity | Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and invested assets	0	0
Accrued investment income	0	0
Deferred acquisition costs	3,215	4,018
Goodwill	0	0
Other assets	0	0
Total assets	3,215	4,018
Investment | Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and invested assets	22,547,498	19,923,204
Accrued investment income	248,991	245,129
Deferred acquisition costs	0	0
Goodwill	0	0
Other assets	0	0
Total assets	$ 22,796,489	$ 20,168,333