New Accounting Standards - Schedule of Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenue:
Premium		$ 1,110,920	$ 1,077,199	$ 2,206,010	$ 2,142,011
Net investment income		261,244	244,712	518,349	489,606
Benefits and expenses:
Life policyholder benefits	[1]	512,664	492,364	1,020,641	987,793
Health policyholder benefits	[2]	195,924	190,075	386,886	379,093
Other policyholder benefits		8,922	8,992	17,910	18,694
Amortization of deferred acquisition costs		94,080	86,185	186,402	170,681
Commissions, premium taxes, and non-deferred acquisition costs		138,459	126,213	276,256	251,722
Income before income taxes		264,506	276,449	538,740	570,625
Income tax benefit (expense)		(49,246)	(52,476)	(99,870)	(109,168)
Net income		$ 215,260	$ 223,973	$ 438,870	$ 461,457
Basic net income per common share (in dollars per share)		$ 2.26	$ 2.28	$ 4.58	$ 4.67
Diluted net income per common share (in dollars per share)		$ 2.24	$ 2.26	$ 4.52	$ 4.63
As Previously Reported
Revenue:
Net investment income			$ 243,642		$ 487,476
Benefits and expenses:
Life policyholder benefits			511,034		1,060,377
Health policyholder benefits			197,218		394,073
Other policyholder benefits			7,074		14,124
Amortization of deferred acquisition costs			155,205		313,589
Commissions, premium taxes, and non-deferred acquisition costs			93,595		184,408
Income before income taxes			216,996		418,611
Income tax benefit (expense)			(39,992)		(77,246)
Net income			$ 177,004		$ 341,365
Basic net income per common share (in dollars per share)			$ 1.80		$ 3.46
Diluted net income per common share (in dollars per share)			$ 1.79		$ 3.43
Adoption Impact
Revenue:
Net investment income			$ 1,070		$ 2,130
Benefits and expenses:
Life policyholder benefits			(18,670)		(72,584)
Health policyholder benefits			(7,143)		(14,980)
Other policyholder benefits			1,918		4,570
Amortization of deferred acquisition costs			(69,020)		(142,908)
Commissions, premium taxes, and non-deferred acquisition costs			32,618		67,314
Income before income taxes			59,453		152,014
Income tax benefit (expense)			(12,484)		(31,922)
Net income			$ 46,969		$ 120,092
Basic net income per common share (in dollars per share)			$ 0.48		$ 1.21
Diluted net income per common share (in dollars per share)			$ 0.47		$ 1.20
Life insurance
Revenue:
Premium		$ 781,733	$ 756,892	$ 1,554,330	$ 1,506,020
Life insurance | As Previously Reported
Revenue:
Premium			759,924		1,514,526
Life insurance | Adoption Impact
Revenue:
Premium			(3,032)		(8,506)
Health premium
Revenue:
Premium		$ 329,187	320,307	$ 651,680	635,991
Health premium | As Previously Reported
Revenue:
Premium			319,189		636,189
Health premium | Adoption Impact
Revenue:
Premium			$ 1,118		$ (198)

[1] Net of remeasurement gain of $2.4 million and $1.7 million for the three months ended June 30, 2023 and 2022, respectively. Net of remeasurement gain of $5.1 million for the six months ended June 30, 2023 and a remeasurement loss of $4.1 million for the same period in 2022.

[2] Net of remeasurement gain of $2.6 million and $2.1 million for the three months ended June 30, 2023 and 2022, respectively. Net of remeasurement gain of $532 thousand and $4.0 million for the six months ended June 30, 2023 and 2022, respectively.