Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating revenues:
Operating revenues	$ 5,336,776	$ 4,531,552	$ 4,443,351
Operating expenses:
Operation and maintenance:	3,895,294	3,256,121	3,135,466
Purchased natural gas sold	421,545	404,153	430,954
Depreciation, depletion and amortization	256,017	220,205	207,486
Taxes, other than income	196,143	168,638	166,673
Electric fuel and purchased power	86,557	80,712	78,724
Total operating expenses	4,855,556	4,129,829	4,019,303
Operating income	481,220	401,723	424,048
Other income (expense)	15,812	(238)	8,767
Interest expense	98,587	84,614	82,788
Income before income taxes	398,445	316,871	350,027
Income taxes	63,279	47,485	65,041
Income from continuing operations	335,166	269,386	284,986
Income (loss) from discontinued operations, net of tax	287	2,932	(3,783)
Net income	335,453	272,318	281,203
Loss on redemption of preferred stock	0	0	600
Dividends declared on preferred stock	0	0	171
Earnings on common stock	$ 335,453	$ 272,318	$ 280,432
Earnings per common share - basic:
Earnings before discontinued operations	$ 1.69	$ 1.38	$ 1.46
Discontinued operations, net of tax	0	0.01	(0.02)
Earnings per common share - basic	1.69	1.39	1.44
Earnings per common share - diluted:
Earnings before discontinued operations	1.69	1.38	1.45
Discontinued operations, net of tax	0	0.01	(0.02)
Earnings per common share - diluted	$ 1.69	$ 1.39	$ 1.43
Weighted average common shares outstanding - basic	198,612	195,720	195,304
Weighted average common shares outstanding - diluted	198,626	196,150	195,687
Regulated:
Operating revenues:
Operating revenues	$ 1,279,304	$ 1,213,227	$ 1,244,759
Operating expenses:
Operation and maintenance:	356,132	340,331	326,687
Nonregulated:
Operating revenues:
Operating revenues	4,057,472	3,318,325	3,198,592
Operating expenses:
Operation and maintenance:	$ 3,539,162	$ 2,915,790	$ 2,808,779