CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Electric	$ 2,961,457	$ 2,671,623	$ 2,319,416
Natural gas	1,209,636	1,067,418	980,913
Other	50,069	66,620	26,121
Total operating revenue	4,221,162	3,805,661	3,326,450
Purchased electricity	1,038,728	784,565	593,719
Electric generation fuel	348,159	282,254	199,107
Residential exchange	(77,715)	(82,225)	(80,294)
Purchased natural gas	500,849	398,553	362,872
Unrealized (gain) loss on derivative instruments, net	(261,177)	(13,785)	26,807
Utility operations and maintenance	665,259	629,864	597,048
Non-utility expense and other	59,804	58,281	43,425
Depreciation and amortization	663,232	704,783	647,755
Conservation amortization	116,942	103,147	99,585
Taxes other than income taxes	389,442	362,527	328,602
Total operating expenses	3,443,523	3,227,964	2,818,626
Operating income (loss)	777,639	577,697	507,824
Other income	45,450	57,483	58,759
Other expense	(19,569)	(14,467)	(23,207)
AFUDC	18,444	16,743	14,827
Interest expense	(347,921)	(352,092)	(373,822)
Income (loss) before income taxes	474,043	285,364	184,381
Income tax (benefit) expense	59,698	24,515	1,664
Net income (loss)	414,345	260,849	182,717
Subsidiaries [Member]
Electric	2,961,457	2,671,623	2,319,416
Natural gas	1,209,636	1,067,418	980,913
Other	45,080	66,620	26,121
Total operating revenue	4,216,173	3,805,661	3,326,450
Purchased electricity	1,038,728	784,565	593,719
Electric generation fuel	348,159	282,254	199,107
Residential exchange	(77,715)	(82,225)	(80,294)
Purchased natural gas	500,849	398,553	362,872
Unrealized (gain) loss on derivative instruments, net	(261,177)	(13,785)	26,807
Utility operations and maintenance	665,259	629,864	597,048
Non-utility expense and other	47,194	56,242	42,266
Depreciation and amortization	657,349	704,372	647,546
Conservation amortization	116,942	103,147	99,585
Taxes other than income taxes	388,123	362,527	328,602
Total operating expenses	3,423,711	3,225,514	2,817,258
Operating income (loss)	792,462	580,147	509,192
Other income	36,684	46,523	46,923
Other expense	(19,569)	(14,467)	(23,207)
AFUDC	18,444	16,743	14,827
Interest expense	(256,774)	(248,624)	(247,213)
Income (loss) before income taxes	571,247	380,322	300,522
Income tax (benefit) expense	80,295	44,259	26,242
Net income (loss)	$ 490,952	$ 336,063	$ 274,280