Segment Information - Summary of Results of Operations Measured as Income Before Federal Income Taxes and Other Items by Operating Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Premiums	$ 536,768	$ 536,237
Other policy revenues	79,605	74,248
Net investment income	115,284	292,346
Realized investment gains	4,148	2,947
Change in investment credit loss	(44,678)	0
Net losses on equity securities	(332,575)	206,377
Other income	11,133	11,538
Total premiums and other revenues	369,685	1,123,693
Policyholder benefits	145,268	168,226
Claims incurred	264,594	263,911
Interest credited to policyholders’ account balances	(4,323)	141,234
Commissions for acquiring and servicing policies	130,435	138,645
Other operating expenses	133,926	133,610
Change in deferred policy acquisition costs	(1,672)	(6,631)
Total benefits, losses and expenses	668,228	838,995
Income (loss) before federal income tax and other items	(298,543)	284,698
Life
Segment Reporting Information [Line Items]
Premiums	89,516	86,468
Other policy revenues	75,540	70,244
Net investment income	45,575	68,756
Realized investment gains	0	0
Change in investment credit loss	0
Net losses on equity securities	0	0
Other income	736	676
Total premiums and other revenues	211,367	226,144
Policyholder benefits	110,466	109,465
Claims incurred	0	0
Interest credited to policyholders’ account balances	(1,903)	20,319
Commissions for acquiring and servicing policies	39,467	37,742
Other operating expenses	47,480	48,978
Change in deferred policy acquisition costs	(7,838)	(4,835)
Total benefits, losses and expenses	187,672	211,669
Income (loss) before federal income tax and other items	23,695	14,475
Annuity
Segment Reporting Information [Line Items]
Premiums	15,509	39,907
Other policy revenues	4,065	4,004
Net investment income	41,541	190,711
Realized investment gains	0	0
Change in investment credit loss	0
Net losses on equity securities	0	0
Other income	638	689
Total premiums and other revenues	61,753	235,311
Policyholder benefits	34,802	58,761
Claims incurred	0	0
Interest credited to policyholders’ account balances	(2,420)	120,915
Commissions for acquiring and servicing policies	10,248	26,866
Other operating expenses	11,876	12,474
Change in deferred policy acquisition costs	7,286	(3,020)
Total benefits, losses and expenses	61,792	215,996
Income (loss) before federal income tax and other items	(39)	19,315
Health
Segment Reporting Information [Line Items]
Premiums	43,086	38,681
Other policy revenues	0	0
Net investment income	2,233	2,420
Realized investment gains	0	0
Change in investment credit loss	0
Net losses on equity securities	0	0
Other income	4,527	5,385
Total premiums and other revenues	49,846	46,486
Policyholder benefits	0	0
Claims incurred	34,885	25,767
Interest credited to policyholders’ account balances	0	0
Commissions for acquiring and servicing policies	8,024	6,878
Other operating expenses	10,629	10,992
Change in deferred policy acquisition costs	(23)	807
Total benefits, losses and expenses	53,515	44,444
Income (loss) before federal income tax and other items	(3,669)	2,042
Property & Casualty
Segment Reporting Information [Line Items]
Premiums	388,657	371,181
Other policy revenues	0	0
Net investment income	16,085	15,022
Realized investment gains	0	0
Change in investment credit loss	0
Net losses on equity securities	0	0
Other income	3,733	2,722
Total premiums and other revenues	408,475	388,925
Policyholder benefits	0	0
Claims incurred	229,709	238,144
Interest credited to policyholders’ account balances	0	0
Commissions for acquiring and servicing policies	72,696	67,159
Other operating expenses	53,004	51,885
Change in deferred policy acquisition costs	(1,097)	417
Total benefits, losses and expenses	354,312	357,605
Income (loss) before federal income tax and other items	54,163	31,320
Corporate & Other
Segment Reporting Information [Line Items]
Premiums	0	0
Other policy revenues	0	0
Net investment income	9,850	15,437
Realized investment gains	4,148	2,947
Change in investment credit loss	(44,678)
Net losses on equity securities	(332,575)	206,377
Other income	1,499	2,066
Total premiums and other revenues	(361,756)	226,827
Policyholder benefits	0	0
Claims incurred	0	0
Interest credited to policyholders’ account balances	0	0
Commissions for acquiring and servicing policies	0	0
Other operating expenses	10,937	9,281
Change in deferred policy acquisition costs	0	0
Total benefits, losses and expenses	10,937	9,281
Income (loss) before federal income tax and other items	$ (372,693)	$ 217,546