Consolidated Statements Of Capitalization - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Stockholders' equity:
Common stock, $0.50 par value	$ 138,438	$ 138,297
Capital in excess of par value	4,142,610	4,137,696
Retained earnings	1,888,521	1,706,675
Treasury stock, at cost	(88,442)	(86,485)
Total stockholders' equity	6,081,127	5,896,183
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Long-term debt of subsidiaries	3,157,791	3,163,008
Total long-term debt	6,970,791	6,938,008
Current portion of long-term debt	67,247	67,415
Long-term debt, excluding current portion	6,903,544	6,870,593
Less: debt issuance costs	47,415	44,508
Long-term debt, excluding current portion, net of debt issuance costs	6,856,129	6,826,085
Total capitalization	12,937,256	12,722,268
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	2,885	2,935
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	7,352	7,538
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	207,403	207,917
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	1,312,241	1,313,932
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	1,242,557	1,245,727
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	313,406	312,745
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	28,061	28,125
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	1,086	1,289
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	258,000	720,000
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 5.375%, due 2034 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Unsecured notes payable	500,000
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 2024 Through 2034 [Member]
Long-term debt of subsidiaries (substantially collateralized by utility plant):
Unsecured notes payable	$ 30,000	$ 30,000