CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating revenue:
Electric	$ 613,386	$ 500,976	$ 1,935,800	$ 1,638,432
Natural Gas	122,808	112,357	710,838	660,997
Other	34,042	7,093	53,074	18,806
Total operating revenue	770,236	620,426	2,699,712	2,318,235
Energy costs:
Purchased electricity	190,928	115,631	558,853	406,860
Electric generation fuel	92,883	54,282	209,749	150,880
Residential exchange	(16,491)	(16,121)	(59,885)	(56,922)
Purchased natural gas	35,518	31,229	253,362	247,362
Unrealized (gain) loss on derivative instruments, net	(88,517)	(39,942)	(172,795)	(3,563)
Utility operations and maintenance	143,873	141,032	454,580	444,074
Non-utility expense and other	24,440	6,340	43,912	35,143
Depreciation & Amortization	162,743	161,209	537,104	462,890
Conservation amortization	19,234	21,295	75,195	69,009
Taxes other than income taxes	68,471	62,163	255,618	236,460
Total operating expenses	633,082	537,118	2,155,693	1,992,193
Operating income (loss)	137,154	83,308	544,019	326,042
Other income (expense):
Other income	14,626	13,050	42,746	43,685
Other expense	(3,317)	(2,160)	(7,177)	(12,910)
Interest charges:
AFUDC	4,337	3,847	11,698	11,404
Interest expense	(84,769)	(88,608)	(264,536)	(284,285)
Income (loss) before income taxes	68,031	9,437	326,750	83,936
Income tax (benefit) expense	18,462	(559)	32,946	2,237
Net income (loss)	49,569	9,996	293,804	81,699
Subsidiaries [Member]
Operating revenue:
Electric	613,386	500,976	1,935,800	1,638,432
Natural Gas	122,808	112,357	710,838	660,997
Other	34,042	7,093	53,074	18,806
Total operating revenue	770,236	620,426	2,699,712	2,318,235
Energy costs:
Purchased electricity	190,928	115,631	558,853	406,860
Electric generation fuel	92,883	54,282	209,749	150,880
Residential exchange	(16,491)	(16,121)	(59,885)	(56,922)
Purchased natural gas	35,518	31,229	253,362	247,362
Unrealized (gain) loss on derivative instruments, net	(88,517)	(39,942)	(172,795)	(3,563)
Utility operations and maintenance	143,873	141,032	454,580	444,074
Non-utility expense and other	23,920	5,510	42,290	33,293
Depreciation & Amortization	162,629	161,155	536,794	462,742
Conservation amortization	19,234	21,295	75,195	69,009
Taxes other than income taxes	68,471	62,163	255,618	236,460
Total operating expenses	632,448	536,234	2,153,761	1,990,195
Operating income (loss)	137,788	84,192	545,951	328,040
Other income (expense):
Other income	11,937	10,424	34,398	34,569
Other expense	(3,317)	(2,160)	(7,177)	(12,910)
Interest charges:
AFUDC	4,337	3,847	11,698	11,404
Interest expense	(57,718)	(61,592)	(182,958)	(184,770)
Income (loss) before income taxes	93,027	34,711	401,912	176,333
Income tax (benefit) expense	18,902	1,649	49,953	16,913
Net income (loss)	$ 74,125	$ 33,062	$ 351,959	$ 159,420