Schedule II - Condensed Financial Information of Registrant (Statements of Cash Flows (Parent Company)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income	$ 1,381,359	$ 1,381,062	$ 1,022,490
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and (accretion) amortization	(20,861)	55,872	129,682
Equity in undistributed earnings of subsidiaries	(16,743)	(145,099)	(220,014)
Stock incentive plans	51,000	49,411	46,680
Change in:
Other liabilities	14,462	19,878	89,467
Net cash from operating activities	2,929,238	2,568,604	2,183,987
Cash from (used in) investing activities:
Proceeds from sale of fixed maturity securities	1,011,195	797,948	1,842,139
Proceeds from maturities and prepayments of fixed maturity securities	3,506,903	4,891,179	6,067,230
Cost of purchases of fixed maturity securities	(6,664,763)	(8,036,680)	(10,716,748)
Change in loans receivable	(29,719)	(83,212)	(27,421)
Change in balances due from security brokers	(33,929)	14,337	(17,983)
Net cash used in investing activities	(1,961,964)	(1,891,355)	(2,989,146)
Cash (used in) from financing activities:
Purchase of common treasury shares	(537,163)	(94,140)	(122,426)
Cash dividends to common stockholders	(501,456)	(235,192)	(355,736)
Other, net	(22,902)	(12,848)	(45,162)
Net cash (used in) from financing activities	(1,062,495)	(771,992)	5,831
Net decrease in cash and cash equivalents	(86,151)	(119,497)	(803,523)
Cash and cash equivalents at beginning of year	1,449,346	1,568,843	2,372,366
Cash and cash equivalents at end of year	1,363,195	1,449,346	1,568,843
Parent Company
Cash flows from operating activities:
Net income	1,381,359	1,381,062	1,022,490
Adjustments to reconcile net income to net cash from operating activities:
Net investment losses (gains)	5,895	(1,007)	(1,474)
Depreciation and (accretion) amortization	(6,753)	4,281	18,761
Equity in undistributed earnings of subsidiaries	(491,501)	(1,511,478)	(763,367)
Tax payments received from subsidiaries	373,504	321,682	328,851
Federal income taxes provided by subsidiaries on a separate return basis	(253,291)	(414,660)	(294,731)
Stock incentive plans	51,000	49,411	48,440
Change in:
Federal income taxes	(15,793)	(40,746)	(22,017)
Other assets	(5,648)	3,163	(33,319)
Other liabilities	(88,954)	87,100	(11,758)
Accrued investment income	1,200	890	755
Net cash from operating activities	951,018	(120,302)	292,631
Cash from (used in) investing activities:
Proceeds from sale of fixed maturity securities	748,825	543,549	402,046
Proceeds from maturities and prepayments of fixed maturity securities	82,075	83,134	654,134
Cost of purchases of fixed maturity securities	(732,685)	(109,289)	(1,071,823)
Change in loans receivable	17,843	(16,249)	(18,227)
Investments in and advances to subsidiaries, net	21,605	(171,062)	(1,411)
Change in balances due from security brokers	(38)	(10,289)	10,487
Net additions to real estate, furniture & equipment	(18)	(432)	(1,496)
Other, net	290	368	95
Net cash used in investing activities	137,897	319,730	(26,195)
Cash (used in) from financing activities:
Net proceeds from issuance of senior notes	0	(914)	1,029,579
Repayment and redemption of debt	0	(426,503)	(400,000)
Purchase of common treasury shares	(537,163)	(94,140)	(122,426)
Cash dividends to common stockholders	(501,456)	(235,192)	(355,736)
Other, net	(25,384)	(23,194)	(30,776)
Net cash (used in) from financing activities	(1,064,003)	(779,943)	120,641
Net decrease in cash and cash equivalents	24,912	(580,515)	387,077
Cash and cash equivalents at beginning of year	103,522	684,037	296,960
Cash and cash equivalents at end of year	$ 128,434	$ 103,522	$ 684,037