Business Segments - Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Jul. 15, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue:
Premium		$ 1,028,067,000	$ 961,817,000	$ 3,054,116,000	$ 2,845,354,000
Net investment income		238,975,000	231,432,000	713,103,000	691,991,000
Other income		321,000	292,000	1,004,000	1,021,000
Total revenue		1,267,363,000	1,193,541,000	3,768,223,000	3,538,366,000
Expenses:
Policy benefits		711,405,000	650,976,000	2,118,735,000	1,909,761,000
Required interest on reserves		0	0	0	0
Required interest on DAC		0	0	0	0
Amortization of acquisition costs		151,593,000	140,843,000	452,607,000	430,840,000
Commissions, premium taxes, and non-deferred acquisition costs		82,774,000	74,614,000	244,752,000	229,691,000
Insurance administrative expense		68,036,000	63,718,000	206,804,000	192,179,000
Parent expense		4,573,000	3,012,000	9,648,000	7,859,000
Stock-based compensation expense		7,776,000	8,667,000	24,298,000	26,655,000
Interest expense		20,886,000	21,674,000	63,833,000	65,295,000
Total benefits and expenses		1,047,043,000	963,504,000	3,120,677,000	2,862,280,000
Subtotal		220,320,000	230,037,000	647,546,000	676,086,000
Non-operating items		2,397,000	1,033,000	7,486,000	4,308,000
Measure of segment profitability (pretax)		222,717,000	231,070,000	655,032,000	680,394,000
Realized gain (loss)—investments		19,789,000	2,135,000	56,600,000	(28,752,000)
Realized loss—redemption of debt	$ (9,300,000)	(9,314,000)	(634,000)	(9,314,000)	(634,000)
Legal proceedings				(5,089,000)	(3,275,000)
Non-operating expenses		(2,397,000)	(1,033,000)	(2,397,000)	(1,033,000)
Income before income taxes		230,795,000	231,538,000	694,832,000	646,700,000
Par Value		$ 1,565,612,000		$ 1,565,612,000
Junior Subordinated Debentures Due 2056
Expenses:
Par Value	$ 300,000,000
Coupon Rate		4.25%		4.25%
Subordinated Debentures | Junior Subordinated Debentures due July 2021
Expenses:
Coupon Rate	6.125%
Life
Revenue:
Premium		$ 728,924,000	674,021,000	$ 2,165,213,000	1,994,473,000
Health
Revenue:
Premium		299,143,000	287,795,000	888,902,000	850,877,000
Annuity
Revenue:
Premium		0	1,000	1,000	4,000
Operating Segments | Life
Revenue:
Premium		728,924,000	674,021,000	2,165,213,000	1,994,473,000
Net investment income		0	0	0	0
Other income		0	0	0	0
Total revenue		728,924,000	674,021,000	2,165,213,000	1,994,473,000
Expenses:
Policy benefits		516,196,000	459,231,000	1,532,298,000	1,340,746,000
Required interest on reserves		(185,295,000)	(175,794,000)	(547,715,000)	(520,207,000)
Required interest on DAC		55,066,000	52,709,000	163,083,000	156,934,000
Amortization of acquisition costs		122,311,000	114,316,000	366,022,000	346,426,000
Commissions, premium taxes, and non-deferred acquisition costs		58,652,000	52,856,000	174,130,000	159,369,000
Insurance administrative expense		0	0	0	0
Parent expense		0	0	0	0
Stock-based compensation expense		0	0	0	0
Interest expense		0	0	0	0
Total benefits and expenses		566,930,000	503,318,000	1,687,818,000	1,483,268,000
Subtotal		161,994,000	170,703,000	477,395,000	511,205,000
Measure of segment profitability (pretax)		161,994,000	170,703,000	477,395,000	511,205,000
Operating Segments | Health
Revenue:
Premium		299,143,000	287,795,000	888,902,000	850,877,000
Net investment income		0	0	0	0
Other income		0	0	0	0
Total revenue		299,143,000	287,795,000	888,902,000	850,877,000
Expenses:
Policy benefits		187,906,000	184,237,000	564,589,000	546,444,000
Required interest on reserves		(25,859,000)	(23,770,000)	(76,288,000)	(69,131,000)
Required interest on DAC		7,203,000	6,689,000	21,242,000	19,790,000
Amortization of acquisition costs		28,799,000	26,026,000	85,138,000	82,905,000
Commissions, premium taxes, and non-deferred acquisition costs		24,116,000	21,753,000	70,602,000	70,304,000
Insurance administrative expense		0	0	0	0
Parent expense		0	0	0	0
Stock-based compensation expense		0	0	0	0
Interest expense		0	0	0	0
Total benefits and expenses		222,165,000	214,935,000	665,283,000	650,312,000
Subtotal		76,978,000	72,860,000	223,619,000	200,565,000
Measure of segment profitability (pretax)		76,978,000	72,860,000	223,619,000	200,565,000
Operating Segments | Annuity
Revenue:
Premium		0	1,000	1,000	4,000
Net investment income		0	0	0	0
Other income		0	0	0	0
Total revenue		0	1,000	1,000	4,000
Expenses:
Policy benefits		7,303,000	7,508,000	21,848,000	22,571,000
Required interest on reserves		(10,034,000)	(10,347,000)	(30,055,000)	(31,135,000)
Required interest on DAC		64,000	81,000	200,000	253,000
Amortization of acquisition costs		483,000	501,000	1,447,000	1,509,000
Commissions, premium taxes, and non-deferred acquisition costs		6,000	5,000	20,000	18,000
Insurance administrative expense		0	0	0	0
Parent expense		0	0	0	0
Stock-based compensation expense		0	0	0	0
Interest expense		0	0	0	0
Total benefits and expenses		(2,178,000)	(2,252,000)	(6,540,000)	(6,784,000)
Subtotal		2,178,000	2,253,000	6,541,000	6,788,000
Measure of segment profitability (pretax)		2,178,000	2,253,000	6,541,000	6,788,000
Operating Segments | Investment
Revenue:
Premium		0	0	0	0
Net investment income		238,975,000	231,432,000	713,103,000	691,991,000
Other income		0	0	0	0
Total revenue		238,975,000	231,432,000	713,103,000	691,991,000
Expenses:
Policy benefits		0	0	0	0
Required interest on reserves		221,188,000	209,911,000	654,058,000	620,473,000
Required interest on DAC		(62,333,000)	(59,479,000)	(184,525,000)	(176,977,000)
Amortization of acquisition costs		0	0	0	0
Commissions, premium taxes, and non-deferred acquisition costs		0	0	0	0
Insurance administrative expense		0	0	0	0
Parent expense		0	0	0	0
Stock-based compensation expense		0	0	0	0
Interest expense		20,886,000	21,674,000	63,833,000	65,295,000
Total benefits and expenses		179,741,000	172,106,000	533,366,000	508,791,000
Subtotal		59,234,000	59,326,000	179,737,000	183,200,000
Measure of segment profitability (pretax)		59,234,000	59,326,000	179,737,000	183,200,000
Corporate & Other
Revenue:
Premium		0	0	0	0
Net investment income		0	0	0	0
Other income		321,000	292,000	1,004,000	1,021,000
Total revenue		321,000	292,000	1,004,000	1,021,000
Expenses:
Policy benefits		0	0	0	0
Required interest on reserves		0	0	0	0
Required interest on DAC		0	0	0	0
Amortization of acquisition costs		0	0	0	0
Commissions, premium taxes, and non-deferred acquisition costs		0	0	0	0
Insurance administrative expense		68,036,000	63,008,000	201,715,000	188,194,000
Parent expense		2,176,000	2,689,000	7,251,000	7,536,000
Stock-based compensation expense		7,776,000	8,667,000	24,298,000	26,655,000
Interest expense		0	0	0	0
Total benefits and expenses		77,988,000	74,364,000	233,264,000	222,385,000
Subtotal		(77,667,000)	(74,072,000)	(232,260,000)	(221,364,000)
Measure of segment profitability (pretax)		(77,667,000)	(74,072,000)	(232,260,000)	(221,364,000)
Adjustments
Revenue:
Premium		0	0	0	0
Net investment income		0	0	0	0
Other income		0	0	0	0
Total revenue		0	0	0	0
Expenses:
Policy benefits		0	0	0	0
Required interest on reserves		0	0	0	0
Required interest on DAC		0	0	0	0
Amortization of acquisition costs		0	0	0	0
Commissions, premium taxes, and non-deferred acquisition costs		0	0	0	0
Insurance administrative expense		0	710,000	5,089,000	3,985,000
Parent expense		2,397,000	323,000	2,397,000	323,000
Stock-based compensation expense		0	0	0	0
Interest expense		0	0	0	0
Total benefits and expenses		2,397,000	1,033,000	7,486,000	4,308,000
Subtotal		(2,397,000)	(1,033,000)	(7,486,000)	(4,308,000)
Non-operating items		2,397,000	1,033,000	7,486,000	4,308,000
Measure of segment profitability (pretax)		$ 0	$ 0	$ 0	$ 0