New Accounting Standards - Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenue:
Premium	$ 1,095,090	$ 1,064,812
Net investment income	257,105	244,894
Benefits and expenses:
Life policyholder benefits	507,977	495,429
Health policyholder benefits	190,962	189,018
Other policyholder benefits	8,988	9,702
Amortization of deferred acquisition costs	92,322	84,496
Commissions, premium taxes, and non-deferred acquisition costs	137,797	125,509
Income before income taxes	274,234	294,176
Income tax benefit (expense)	(50,624)	(56,692)
Net income	$ 223,610	$ 237,484
Basic net income per common share (in dollars per share)	$ 2.32	$ 2.39
Diluted net income per common share (in dollars per share)	$ 2.28	$ 2.37
Previously Reported
Revenue:
Net investment income		$ 243,834
Benefits and expenses:
Life policyholder benefits		549,343
Health policyholder benefits		196,855
Other policyholder benefits		7,050
Amortization of deferred acquisition costs		158,384
Commissions, premium taxes, and non-deferred acquisition costs		90,813
Income before income taxes		201,615
Income tax benefit (expense)		(37,254)
Net income		$ 164,361
Basic net income per common share (in dollars per share)		$ 1.66
Diluted net income per common share (in dollars per share)		$ 1.64
Revision of Prior Period, Adjustment
Revenue:
Net investment income		$ 1,060
Benefits and expenses:
Life policyholder benefits		(53,914)
Health policyholder benefits		(7,837)
Other policyholder benefits		2,652
Amortization of deferred acquisition costs		(73,888)
Commissions, premium taxes, and non-deferred acquisition costs		34,696
Income before income taxes		92,561
Income tax benefit (expense)		(19,438)
Net income		$ 73,123
Basic net income per common share (in dollars per share)		$ 0.73
Diluted net income per common share (in dollars per share)		$ 0.73
Life insurance
Revenue:
Premium	$ 772,597	$ 749,128
Life insurance | Previously Reported
Revenue:
Premium		754,602
Life insurance | Revision of Prior Period, Adjustment
Revenue:
Premium		(5,474)
Health premium
Revenue:
Premium	$ 322,493	315,684
Health premium | Previously Reported
Revenue:
Premium		317,000
Health premium | Revision of Prior Period, Adjustment
Revenue:
Premium		$ (1,316)