Schedule II. Condensed Financial Information of Registrant (Condensed Statement of Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Condensed Financial Statements, Captions [Line Items]
Net income	$ 1,070,762	$ 970,755	$ 894,386
Other, net	(17,582)	(24,799)	44,480
Cash provided from (used for) operating activities	1,402,440	1,482,425	1,422,194
Cash provided from (used for) investing activities:
Net decrease (increase) in short-term investments	(3,295)	32,381	(44,976)
Loaned money to affiliates	(71,045)	(49,553)	(27,929)
Cash provided from (used for) investing activities	(641,516)	(926,149)	(943,015)
Cash provided from (used for) financing activities:
Repayment of debt	0	(165,612)	(150,000)
Payment for debt issuance costs	(7,253)	(757)	(5,272)
Proceeds from commercial paper with original maturities greater than 90 days	484,726	0	0
Repayment of commercial paper with original maturities greater than 90 days	(372,011)	0	0
Issuance of stock	51,786	114,080	106,592
Acquisitions of treasury stock	(1,002,109)	(511,100)	(454,638)
Payment of dividends	(85,485)	(84,116)	(80,547)
Cash provided from (used for) financing activities	(715,835)	(541,487)	(492,453)
Net increase (decrease) in cash	62,169	10,597	396
Cash at end of year	165,325	103,156	92,559
Cash at beginning of year	103,156	92,559	92,163
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net income	1,070,762	970,755	894,386
Equity in earnings of affiliates	(1,155,705)	(1,024,323)	(962,985)
Cash dividends from subsidiaries	692,690	459,535	407,042
Other, net	55,243	33,846	26,444
Cash provided from (used for) operating activities	662,990	439,813	364,887
Cash provided from (used for) investing activities:
Net decrease (increase) in short-term investments	(28,000)	13,996	(15,001)
Investment in subsidiaries	(12)	0	(10,010)
Acquisition of investments	(2,850)	(3,950)	(2,000)
Disposition of investments	1	0	0
Loaned money to affiliates	(557,016)	(479,629)	(846,002)
Repayments from affiliates	394,925	505,929	886,002
Additions to properties	(19,147)	(7,400)	0
Cash provided from (used for) investing activities	(212,099)	28,946	12,989
Cash provided from (used for) financing activities:
Repayment of debt	0	(165,612)	(300,000)
Proceeds from issuance of debt	530,000	170,000	400,000
Payment for debt issuance costs	(7,253)	(757)	(5,272)
Net change in commercial paper held less than 90 days	(13,878)	32,961	(46,289)
Proceeds from commercial paper with original maturities greater than 90 days	484,726	0	0
Repayment of commercial paper with original maturities greater than 90 days	(372,011)	0	0
Issuance of stock	51,756	114,080	111,970
Acquisitions of treasury stock	(1,002,109)	(511,100)	(454,638)
Borrowed money from affiliate	349,000	290,500	22,400
Repayments to affiliates	(296,600)	(290,500)	(22,400)
Payment of dividends	(108,755)	(107,386)	(103,817)
Cash provided from (used for) financing activities	(385,124)	(467,814)	(398,046)
Net increase (decrease) in cash	65,767	945	(20,170)
Cash at end of year	66,770	1,003	58
Cash at beginning of year	$ 1,003	$ 58	$ 20,228