Business Segments - Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Jul. 15, 2021	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue:
Premium			$ 4,099,887,000	$ 3,813,905,000	$ 3,595,134,000
Net investment income			952,447,000	927,062,000	910,459,000
Other income			1,216,000	1,325,000	1,318,000
Total revenue			5,053,550,000	4,742,292,000	4,506,911,000
Expenses:
Policy obligations			2,859,616,000	2,572,884,000	2,357,349,000
Required interest on reserves			0	0	0
Required interest on DAC			0	0	0
Amortization of acquisition costs			603,838,000	575,770,000	551,726,000
Commissions, premium taxes, and non-deferred acquisition costs			331,510,000	304,841,000	298,047,000
Insurance administrative expense			282,029,000	254,932,000	249,079,000
Parent expense			9,728,000	10,214,000	10,903,000
Stock-based compensation expense			30,272,000	35,892,000	44,843,000
Interest expense			83,486,000	86,704,000	84,306,000
Total benefits and expenses			4,200,479,000	3,841,237,000	3,596,253,000
Subtotal			853,071,000	901,055,000	910,658,000
Non-operating items			11,898,000	4,308,000	9,401,000
Measure of segment profitability (pretax)			864,969,000	905,363,000	920,059,000
Realized gain (loss)—investments			68,633,000	(3,737,000)	20,621,000
Realized loss—redemption of debt	$ (9,300,000)		(9,314,000)	(634,000)	0
Administrative settlements		$ (1,325,000)			(400,000)
Legal proceedings			(8,139,000)	(3,275,000)	(8,358,000)
Non-operating expenses			(2,434,000)	(1,033,000)	(643,000)
Income before income taxes			912,390,000	896,684,000	931,279,000
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			$ 2,898,210,000	2,672,804,000	2,517,784,000
Health
Revenue:
Premium			1,201,676,000	1,141,097,000	1,077,346,000
Annuity
Revenue:
Premium			1,000	4,000	4,000
Operating Segments | Life
Revenue:
Premium			2,898,210,000	2,672,804,000	2,517,784,000
Net investment income			0	0	0
Other income			0	0	0
Total revenue			2,898,210,000	2,672,804,000	2,517,784,000
Expenses:
Policy obligations			2,070,485,000	1,809,373,000	1,638,053,000
Required interest on reserves			(735,282,000)	(698,112,000)	(666,168,000)
Required interest on DAC			218,575,000	210,152,000	202,502,000
Amortization of acquisition costs			486,724,000	463,586,000	436,881,000
Commissions, premium taxes, and non-deferred acquisition costs			234,033,000	212,859,000	203,052,000
Insurance administrative expense			0	0	0
Parent expense			0	0	0
Stock-based compensation expense			0	0	0
Interest expense			0	0	0
Total benefits and expenses			2,274,535,000	1,997,858,000	1,814,320,000
Subtotal			623,675,000	674,946,000	703,464,000
Measure of segment profitability (pretax)			623,675,000	674,946,000	703,464,000
Operating Segments | Health
Revenue:
Premium			1,201,676,000	1,141,097,000	1,077,346,000
Net investment income			0	0	0
Other income			0	0	0
Total revenue			1,201,676,000	1,141,097,000	1,077,346,000
Expenses:
Policy obligations			758,745,000	733,481,000	687,764,000
Required interest on reserves			(102,574,000)	(93,475,000)	(87,289,000)
Required interest on DAC			28,556,000	26,586,000	25,435,000
Amortization of acquisition costs			115,194,000	110,177,000	112,825,000
Commissions, premium taxes, and non-deferred acquisition costs			97,453,000	91,959,000	94,973,000
Insurance administrative expense			0	0	0
Parent expense			0	0	0
Stock-based compensation expense			0	0	0
Interest expense			0	0	0
Total benefits and expenses			897,374,000	868,728,000	833,708,000
Subtotal			304,302,000	272,369,000	243,638,000
Measure of segment profitability (pretax)			304,302,000	272,369,000	243,638,000
Operating Segments | Annuity
Revenue:
Premium			1,000	4,000	4,000
Net investment income			0	0	0
Other income			0	0	0
Total revenue			1,000	4,000	4,000
Expenses:
Policy obligations			29,061,000	30,030,000	31,532,000
Required interest on reserves			(39,966,000)	(41,413,000)	(43,522,000)
Required interest on DAC			258,000	328,000	494,000
Amortization of acquisition costs			1,920,000	2,007,000	2,020,000
Commissions, premium taxes, and non-deferred acquisition costs			24,000	23,000	22,000
Insurance administrative expense			0	0	0
Parent expense			0	0	0
Stock-based compensation expense			0	0	0
Interest expense			0	0	0
Total benefits and expenses			(8,703,000)	(9,025,000)	(9,454,000)
Subtotal			8,704,000	9,029,000	9,458,000
Measure of segment profitability (pretax)			8,704,000	9,029,000	9,458,000
Operating Segments | Investment
Revenue:
Premium			0	0	0
Net investment income			952,447,000	927,062,000	910,459,000
Other income			0	0	0
Total revenue			952,447,000	927,062,000	910,459,000
Expenses:
Policy obligations			0	0	0
Required interest on reserves			877,822,000	833,000,000	796,979,000
Required interest on DAC			(247,389,000)	(237,066,000)	(228,431,000)
Amortization of acquisition costs			0	0	0
Commissions, premium taxes, and non-deferred acquisition costs			0	0	0
Insurance administrative expense			0	0	0
Parent expense			0	0	0
Stock-based compensation expense			0	0	0
Interest expense			83,486,000	86,704,000	84,306,000
Total benefits and expenses			713,919,000	682,638,000	652,854,000
Subtotal			238,528,000	244,424,000	257,605,000
Measure of segment profitability (pretax)			238,528,000	244,424,000	257,605,000
Corporate & Other
Revenue:
Premium			0	0	0
Net investment income			0	0	0
Other income			1,216,000	1,325,000	1,318,000
Total revenue			1,216,000	1,325,000	1,318,000
Expenses:
Policy obligations			0	0	0
Required interest on reserves			0	0	0
Required interest on DAC			0	0	0
Amortization of acquisition costs			0	0	0
Commissions, premium taxes, and non-deferred acquisition costs			0	0	0
Insurance administrative expense			271,631,000	250,947,000	240,321,000
Parent expense			9,553,000	9,891,000	10,260,000
Stock-based compensation expense			30,272,000	35,892,000	44,843,000
Interest expense			0	0	0
Total benefits and expenses			311,456,000	296,730,000	295,424,000
Subtotal			(310,240,000)	(295,405,000)	(294,106,000)
Measure of segment profitability (pretax)			(310,240,000)	(295,405,000)	(294,106,000)
Adjustments
Revenue:
Premium			0	0	0
Net investment income			0	0	0
Other income			0	0	0
Total revenue			0	0	0
Expenses:
Policy obligations			1,325,000	0	0
Required interest on reserves			0	0	0
Required interest on DAC			0	0	0
Amortization of acquisition costs			0	0	0
Commissions, premium taxes, and non-deferred acquisition costs			0	0	0
Insurance administrative expense			10,398,000	3,985,000	8,758,000
Parent expense			175,000	323,000	643,000
Stock-based compensation expense			0	0	0
Interest expense			0	0	0
Total benefits and expenses			11,898,000	4,308,000	9,401,000
Subtotal			(11,898,000)	(4,308,000)	(9,401,000)
Non-operating items			11,898,000	4,308,000	9,401,000
Measure of segment profitability (pretax)			$ 0	$ 0	$ 0