New Accounting Standards - Schedule of Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue:
Premium		$ 1,119,335	$ 1,079,282	$ 3,325,345	$ 3,221,293
Net investment income		266,926	246,711	785,275	736,317
Benefits and expenses:
Life policyholder benefits	[1]	515,676	545,933	1,536,317	1,533,726
Health policyholder benefits	[2]	193,790	182,409	580,676	561,502
Other policyholder benefits		9,578	9,234	27,488	27,928
Amortization of deferred acquisition costs		95,757	88,012	282,159	258,693
Commissions, premium taxes, and non-deferred acquisition costs		138,677	124,768	414,933	376,490
Income before income taxes		318,815	234,776	857,555	805,401
Income tax benefit (expense)		(61,732)	(44,190)	(161,602)	(153,358)
Net income		$ 257,083	$ 190,586	$ 695,953	$ 652,043
Basic net income per common share (in dollars per share)		$ 2.72	$ 1.96	$ 7.29	$ 6.64
Diluted net income per common share (in dollars per share)		$ 2.68	$ 1.94	$ 7.20	$ 6.58
As Previously Reported
Revenue:
Net investment income			$ 245,625		$ 733,101
Benefits and expenses:
Life policyholder benefits			494,627		1,555,004
Health policyholder benefits			198,415		592,488
Other policyholder benefits			6,986		21,110
Amortization of deferred acquisition costs			156,129		469,718
Commissions, premium taxes, and non-deferred acquisition costs			93,028		277,436
Income before income taxes			229,983		648,594
Income tax benefit (expense)			(43,204)		(120,450)
Net income			$ 186,779		$ 528,144
Basic net income per common share (in dollars per share)			$ 1.92		$ 5.38
Diluted net income per common share (in dollars per share)			$ 1.90		$ 5.33
Adoption Impact
Revenue:
Net investment income			$ 1,086		$ 3,216
Benefits and expenses:
Life policyholder benefits			51,306		(21,278)
Health policyholder benefits			(16,006)		(30,986)
Other policyholder benefits			2,248		6,818
Amortization of deferred acquisition costs			(68,117)		(211,025)
Commissions, premium taxes, and non-deferred acquisition costs			31,740		99,054
Income before income taxes			4,793		156,807
Income tax benefit (expense)			(986)		(32,908)
Net income			$ 3,807		$ 123,899
Basic net income per common share (in dollars per share)			$ 0.04		$ 1.26
Diluted net income per common share (in dollars per share)			$ 0.04		$ 1.25
Life insurance
Revenue:
Premium		$ 788,099	$ 758,875	$ 2,342,429	$ 2,264,895
Life insurance | As Previously Reported
Revenue:
Premium			755,115		2,269,641
Life insurance | Adoption Impact
Revenue:
Premium			3,760		(4,746)
Health premium
Revenue:
Premium		$ 331,236	320,406	$ 982,916	956,397
Health premium | As Previously Reported
Revenue:
Premium			319,289		955,478
Health premium | Adoption Impact
Revenue:
Premium			$ 1,117		$ 919

[1] et of the total remeasurement, including both the impact of assumption changes and the effect of actual to expected experience adjustments, resulting in a $11.3 million gain and a $45.2 million loss for the three months ended September 30, 2023 and 2022, respectively. Net of the total remeasurement gain of $16.5 million for the nine months ended September 30, 2023 and the total remeasurement loss of $49.3 million for the same period in 2022.

[2] $7.8 million gain and $9.7 million gain for the three months ended September 30, 2023 and 2022, respectively. Net of the total remeasurement gain of $8.3 million and $13.8 million for the nine months ended September 30, 2023 and 2022, respectively.