Schedule III - Supplementary Insurance Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	$ 1,423,007	$ 1,497,261	$ 1,373,844
Future policy benefits, policyholders’ account balances, policy and contract claims and other policyholder funds	19,517,754	18,884,849	18,239,714
Unearned premiums	933,559	908,856	875,294
Premium revenue	2,182,794	2,228,193	2,067,202
Net investment income	1,077,406	858,367	966,077
Benefits, claims, losses and settlement expenses	1,818,994	1,879,972	1,718,203
Amortization of deferred policy acquisition costs	530,509	480,157	444,351
Other operating expenses	524,888	497,011	485,340
Premiums written	1,546,144	1,514,563	1,414,024
Life
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	852,900	839,133	791,276
Future policy benefits, policyholders’ account balances, policy and contract claims and other policyholder funds	5,293,970	5,158,377	5,432,688
Unearned premiums	27,080	29,901	33,298
Premium revenue	359,419	350,012	328,570
Net investment income	263,788	233,181	245,835
Benefits, claims, losses and settlement expenses	449,252	417,702	410,152
Amortization of deferred policy acquisition costs	113,300	97,263	74,068
Other operating expenses	190,104	190,835	190,482
Annuity
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	415,380	499,588	426,497
Future policy benefits, policyholders’ account balances, policy and contract claims and other policyholder funds	12,856,209	12,372,418	11,533,813
Premium revenue	147,139	231,027	222,207
Net investment income	663,895	467,788	573,789
Benefits, claims, losses and settlement expenses	218,576	290,611	270,970
Amortization of deferred policy acquisition costs	79,746	57,468	74,750
Other operating expenses	50,507	46,859	44,486
Health
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	32,578	33,960	36,806
Future policy benefits, policyholders’ account balances, policy and contract claims and other policyholder funds	282,592	319,789	282,872
Unearned premiums	34,862	37,261	40,665
Premium revenue	165,035	180,414	156,436
Net investment income	9,467	9,376	9,538
Benefits, claims, losses and settlement expenses	109,013	122,547	103,037
Amortization of deferred policy acquisition costs	21,322	15,436	15,227
Other operating expenses	41,475	41,819	38,475
Property & Casualty
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	122,149	124,580	119,265
Future policy benefits, policyholders’ account balances, policy and contract claims and other policyholder funds	1,084,983	1,034,265	990,341
Unearned premiums	871,617	841,694	801,331
Premium revenue	1,511,201	1,466,740	1,359,989
Net investment income	64,263	62,320	61,688
Benefits, claims, losses and settlement expenses	1,042,153	1,049,112	934,044
Amortization of deferred policy acquisition costs	316,141	309,990	280,306
Other operating expenses	201,580	186,019	177,345
Premiums written	1,546,144	1,514,563	1,414,024
Corporate & Other
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net investment income	75,993	85,702	75,227
Amortization of deferred policy acquisition costs	0
Other operating expenses	$ 41,222	$ 31,479	$ 34,552