CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating revenue:
Electric	$ 758,592	$ 669,090
Natural Gas	392,906	371,031
Other	8,588	6,009
Total operating revenue	1,160,086	1,046,130
Energy costs:
Purchased electricity	205,410	165,742
Electric generation fuel	60,418	63,624
Residential exchange	(25,802)	(24,634)
Purchased natural gas	155,015	154,876
Unrealized (gain) loss on derivative instruments, net	(23,002)	48,541
Utility operations and maintenance	160,540	154,922
Non-utility expense and other	9,906	12,962
Depreciation & Amortization	208,431	164,816
Conservation amortization	34,060	27,393
Taxes other than income taxes	110,310	105,504
Total operating expenses	895,286	873,746
Operating income (loss)	264,800	172,384
Other income (expense):
Other income	13,630	14,059
Other expense	(1,510)	(2,282)
Interest charges:
AFUDC	3,586	3,643
Interest expense	(89,360)	(88,884)
Income (loss) before income taxes	191,146	98,920
Income tax (benefit) expense	2,153	3,984
Net income (loss)	188,993	94,936
Subsidiaries [Member]
Operating revenue:
Electric	758,592	669,090
Natural Gas	392,906	371,031
Other	8,588	6,009
Total operating revenue	1,160,086	1,046,130
Energy costs:
Purchased electricity	205,410	165,742
Electric generation fuel	60,418	63,624
Residential exchange	(25,802)	(24,634)
Purchased natural gas	155,015	154,876
Unrealized (gain) loss on derivative instruments, net	(23,002)	48,541
Utility operations and maintenance	160,540	154,922
Non-utility expense and other	9,418	12,735
Depreciation & Amortization	208,362	164,771
Conservation amortization	34,060	27,393
Taxes other than income taxes	110,310	105,504
Total operating expenses	894,729	873,474
Operating income (loss)	265,357	172,656
Other income (expense):
Other income	11,034	11,283
Other expense	(1,510)	(2,282)
Interest charges:
AFUDC	3,586	3,643
Interest expense	(62,371)	(60,714)
Income (loss) before income taxes	216,096	124,586
Income tax (benefit) expense	16,626	13,265
Net income (loss)	$ 199,470	$ 111,321