Business Segments - Schedule of Reconciliation of Segment Operating Information to Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenue:
Premium	$ 4,666,272	$ 4,456,017	$ 4,310,241
Net investment income	1,135,631	1,056,884	991,800
Segment revenue	5,801,903	5,512,901	5,302,041
Annuity premium income			1
Other income	354	308	1,246
Realized gains (losses)	(24,188)	(65,676)	(76,548)
Total revenue	5,778,069	5,447,533	5,226,740
Expenses:
Policy obligations	2,873,523	2,836,212	2,792,931
Required interest on reserves	28,769	38,224	44,836
Amortization of acquisition costs	408,447	378,024	347,026
Commissions	318,572	295,870	285,468
Premium taxes	96,781	91,011	86,262
Non-deferred acquisition costs	186,387	172,269	134,267
Segment profit or (loss)	1,889,424	1,701,291	1,611,251
Insurance administrative expenses:
Salaries	129,369	119,699	129,711
Other employee costs	36,176	35,905	42,319
Information technology costs	80,555	64,998	55,526
Legal costs	30,478	15,335	12,056
Other administrative costs	65,852	65,224	59,729
Parent expense	12,400	10,866	11,156
Stock-based compensation expense	40,118	30,736	35,650
Interest expense	127,092	102,316	90,395
Legal proceedings	21,575	900	2,496
Non-operating expenses	2,620	4,170	5,311
Annuity	(7,282)	(8,492)	(10,510)
Insurance Administrative Expenses, Total	4,451,432	4,253,267	4,124,629
Income before income taxes	1,326,637	1,194,266	1,102,111
Life
Revenue:
Premium	3,261,347	3,137,244	3,027,824
Net investment income	0	0	0
Segment revenue	3,261,347	3,137,244	3,027,824
Expenses:
Policy obligations	2,000,977	2,050,789	2,035,693
Required interest on reserves	(811,147)	(772,701)	(735,688)
Amortization of acquisition costs	356,223	327,426	298,841
Commissions	159,703	145,678	140,283
Premium taxes	68,360	64,571	61,609
Non-deferred acquisition costs	134,634	128,509	97,561
Segment profit or (loss)	1,352,597	1,192,972	1,129,525
Health
Revenue:
Premium	1,404,925	1,318,773	1,282,417
Net investment income	0	0	0
Segment revenue	1,404,925	1,318,773	1,282,417
Expenses:
Policy obligations	851,577	776,362	752,866
Required interest on reserves	(110,342)	(106,516)	(102,315)
Amortization of acquisition costs	52,224	50,598	48,185
Commissions	158,869	150,192	145,185
Premium taxes	28,421	26,440	24,653
Non-deferred acquisition costs	51,753	43,760	36,706
Segment profit or (loss)	372,423	377,937	377,137
Investment
Revenue:
Premium	0	0	0
Net investment income	1,135,631	1,056,884	991,800
Segment revenue	1,135,631	1,056,884	991,800
Expenses:
Policy obligations	20,969	9,061	4,372
Required interest on reserves	950,258	917,441	882,839
Amortization of acquisition costs	0	0	0
Commissions	0	0	0
Premium taxes	0	0	0
Non-deferred acquisition costs	0	0	0
Segment profit or (loss)	$ 164,404	$ 130,382	$ 104,589