Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating revenues:
Operating revenues	$ 5,532,750	$ 5,336,776	$ 4,531,552
Operating expenses:
Operation and maintenance:	4,028,262	3,895,294	3,256,121
Purchased natural gas sold	390,269	421,545	404,153
Depreciation, depletion and amortization	285,100	256,017	220,205
Taxes, other than income	217,253	196,143	168,638
Electric fuel and purchased power	66,941	86,557	80,712
Total operating expenses	4,987,825	4,855,556	4,129,829
Operating income	544,925	481,220	401,723
Other income (expense)	26,711	15,812	(238)
Interest expense	96,519	98,587	84,614
Income before income taxes	475,117	398,445	316,871
Income taxes	84,590	63,279	47,485
Income from continuing operations	390,527	335,166	269,386
Income (loss) from discontinued operations, net of tax	(322)	287	2,932
Net income	$ 390,205	$ 335,453	$ 272,318
Earnings per share - basic:
Income from continuing operations	$ 1.95	$ 1.69	$ 1.38
Discontinued operations, net of tax	0	0	0.01
Earnings per share - basic	1.95	1.69	1.39
Earnings per share - diluted:
Income from continuing operations	1.95	1.69	1.38
Discontinued operations, net of tax	0	0	0.01
Earnings per share - diluted	$ 1.95	$ 1.69	$ 1.39
Weighted average common shares outstanding - basic	200,502	198,612	195,720
Weighted Average Number of Shares Outstanding, Diluted	200,571	198,626	196,150
Regulated Operation
Operating revenues:
Operating revenues	$ 1,249,146	$ 1,279,304	$ 1,213,227
Operating expenses:
Operation and maintenance:	353,184	356,132	340,331
Income from continuing operations	135,103	122,535	111,637
Unregulated Operation
Operating revenues:
Operating revenues	4,283,604	4,057,472	3,318,325
Operating expenses:
Operation and maintenance:	3,675,078	3,539,162	2,915,790
Income from continuing operations	$ 255,424	$ 212,631	$ 157,749