CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Utility revenues:
Utility revenues, exclusive of alternative revenue programs	$ 301,176	$ 273,975	$ 713,358	$ 667,795
Alternative revenue programs	(3,069)	4,362	(2,570)	(51)
Total utility revenues	298,107	278,337	710,788	667,744
Non-utility revenues	148	255	337	1,078
Total operating revenues	298,255	278,592	711,125	668,822
Utility operating expenses:
Resource costs	90,678	67,965	225,257	197,512
Other operating expenses	94,053	86,204	181,608	180,700
Depreciation and amortization	56,066	63,908	111,287	115,329
Taxes other than income taxes	24,474	24,742	56,783	55,720
Non-utility operating expenses:
Other operating expenses	1,159	659	2,343	2,019
Depreciation and amortization	73	188	200	423
Total operating expenses	266,503	243,666	577,478	551,703
Income from operations	31,752	34,926	133,647	117,119
Interest expense	26,131	25,625	52,435	51,972
Interest expense to affiliated trusts	106	208	215	478
Capitalized interest	(916)	(972)	(1,931)	(1,970)
Other expense (income)-net	(10,041)	531	(13,725)	149
Income before income taxes	16,472	9,534	96,653	66,490
Income tax expense (benefit)	2,398	(7,919)	14,562	613
Net income	$ 14,074	$ 17,453	$ 82,091	$ 65,877
Weighted-average common shares outstanding (thousands), basic	69,404	67,481	69,348	67,360
Weighted-average common shares outstanding (thousands), diluted	69,534	67,589	69,520	67,485
Earnings per common share:
Basic	$ 0.20	$ 0.26	$ 1.18	$ 0.98
Diluted	$ 0.20	$ 0.26	$ 1.18	$ 0.98