Consolidated Statements Of Capitalization - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Stockholders' equity:
Common stock, $0.50 par value	$ 138,235	$ 133,486
Capital in excess of par value	4,131,834	3,793,262
Retained earnings	1,739,271	1,534,331
Treasury stock, at cost	(86,783)	(83,693)
Total stockholders' equity	5,922,557	5,377,386
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	3,317,873	3,062,395
Total long-term debt	6,719,873	6,617,395
Current portion of long-term debt	218,619	199,356
Long-term debt, excluding current portion	6,501,254	6,418,039
Less: debt issuance costs	45,214	46,982
Long-term debt, excluding current portion, net of debt issuance costs	6,456,040	6,371,057
Total capitalization	12,378,597	11,748,443
Long-Term Debt Of Subsidiaries 0.00% To 0.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	1,411	1,875
Long-Term Debt Of Subsidiaries 1.00% To 1.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	7,730	8,369
Long-Term Debt Of Subsidiaries 2.00% To 2.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	208,425	209,755
Long-Term Debt Of Subsidiaries 3.00% To 3.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	1,315,519	1,351,432
Long-Term Debt Of Subsidiaries 4.00% To 4.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	1,398,614	1,403,313
Long-Term Debt Of Subsidiaries 5.00% To 5.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	313,698	14,357
Long-Term Debt Of Subsidiaries 6.00% To 6.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	31,000	31,000
Long-Term Debt Of Subsidiaries 7.00% To 7.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	28,188	28,378
Long-Term Debt Of Subsidiaries 8.00% To 8.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	1,488	2,116
Long-Term Debt Of Subsidiaries 9.00% To 9.99% [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	11,800	11,800
Revolving Credit Agreement, Due 2027 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Notes payable to bank under revolving credit agreement, variable rate, due 2027	347,000	490,000
Notes At 2.40% Due 2031 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Unsecured notes payable	400,000	400,000
Notes At 2.704% Due 2030 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Unsecured notes payable	500,000	500,000
Notes Ranging From 3.01% To 3.59% Due 2029 Through 2050 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Unsecured notes payable	1,125,000	1,125,000
Notes At 4.28%, Due 2049 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Unsecured notes payable	500,000	500,000
Notes At 5.30%, Due 2052 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Unsecured notes payable	500,000	500,000
Notes At 5.95%, Due 2023 Through 2034 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Unsecured notes payable	$ 30,000	$ 40,000