Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating revenues:
Operating revenues	$ 5,680,733	$ 5,532,750	$ 5,336,776
Operating expenses:
Operation and maintenance:	4,078,623	4,028,262	3,895,294
Purchased natural gas sold	483,118	390,269	421,545
Depreciation, depletion and amortization	299,214	285,100	256,017
Taxes, other than income	211,454	217,253	196,143
Electric fuel and purchased power	74,105	66,941	86,557
Total operating expenses	5,146,514	4,987,825	4,855,556
Operating income	534,219	544,925	481,220
Other income	26,416	26,711	15,812
Interest expense	93,984	96,519	98,587
Income before income taxes	466,651	475,117	398,445
Income taxes	88,920	84,590	63,279
Income from continuing operations	377,731	390,527	335,166
Income (loss) from discontinued operations, net of tax	400	(322)	287
Net income	$ 378,131	$ 390,205	$ 335,453
Earnings per share - basic:
Income from continuing operations	$ 1.87	$ 1.95	$ 1.69
Discontinued operations, net of tax	0	0	0
Earnings per share - basic	1.87	1.95	1.69
Earnings per share - diluted:
Income from continuing operations	1.87	1.95	1.69
Discontinued operations, net of tax	0	0	0
Earnings per share - diluted	$ 1.87	$ 1.95	$ 1.69
Weighted average common shares outstanding - basic	202,076	200,502	198,612
Weighted Average Number of Shares Outstanding, Diluted	202,383	200,571	198,626
Regulated Operation
Operating revenues:
Operating revenues	$ 1,390,343	$ 1,249,146	$ 1,279,304
Operating expenses:
Operation and maintenance:	366,586	353,184	356,132
Income from continuing operations	143,085	135,103	122,535
Nonregulated Operation
Operating revenues:
Operating revenues	4,290,390	4,283,604	4,057,472
Operating expenses:
Operation and maintenance:	3,712,037	3,675,078	3,539,162
Income from continuing operations	$ 234,646	$ 255,424	$ 212,631