CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating revenue:
Electric	$ 468,366	$ 510,742	$ 1,137,456	$ 1,309,670
Natural gas	177,609	153,457	548,640	458,125
Other	5,704	6,731	11,713	17,974
Total operating revenue	651,679	670,930	1,697,809	1,785,769
Energy costs:
Purchased electricity	125,487	124,001	291,229	394,703
Electric generation fuel	32,974	37,601	96,598	114,800
Residential exchange	(16,167)	(15,972)	(40,801)	(41,135)
Purchased natural gas	61,257	41,116	216,133	140,503
Unrealized (gain) loss on derivative instruments, net	(12,162)	30,332	36,379	15,145
Utility operations and maintenance	148,120	149,424	303,042	307,379
Non-utility expense and other	15,841	10,620	28,803	24,377
Depreciation & amortization	136,865	164,715	301,681	345,412
Conservation amortization	20,321	20,029	47,714	53,315
Taxes other than income taxes	68,793	69,949	174,297	178,695
Total operating expenses	581,329	631,815	1,455,075	1,533,194
Operating income(loss)	70,350	39,115	242,734	252,575
Other income (expense):
Other income	16,576	15,439	30,635	29,003
Other expense	(8,468)	(1,825)	(10,750)	(3,601)
Interest charges:
AFUDC	3,914	3,570	7,557	6,920
Interest expense	(106,793)	(87,770)	(195,677)	(175,786)
Income (loss) before income taxes	(24,421)	(31,471)	74,499	109,111
Income tax (benefit) expense	(1,188)	1,481	2,796	9,909
Net income (loss)	(23,233)	(32,952)	71,703	99,202
Subsidiaries [Member]
Operating revenue:
Electric	468,366	510,742	1,137,456	1,309,670
Natural gas	177,609	153,457	548,640	458,125
Other	5,704	6,731	11,713	17,974
Total operating revenue	651,679	670,930	1,697,809	1,785,769
Energy costs:
Purchased electricity	125,487	124,001	291,229	394,703
Electric generation fuel	32,974	37,601	96,598	114,800
Residential exchange	(16,167)	(15,972)	(40,801)	(41,135)
Purchased natural gas	61,257	41,116	216,133	140,503
Unrealized (gain) loss on derivative instruments, net	(12,162)	30,332	36,379	15,145
Utility operations and maintenance	148,120	149,424	303,042	307,379
Non-utility expense and other	15,048	9,978	27,783	23,055
Depreciation & amortization	136,816	164,692	301,587	345,370
Conservation amortization	20,321	20,029	47,714	53,315
Taxes other than income taxes	68,793	69,949	174,297	178,695
Total operating expenses	580,487	631,150	1,453,961	1,531,830
Operating income(loss)	71,192	39,780	243,848	253,939
Other income (expense):
Other income	12,862	12,412	24,145	22,961
Other expense	(8,468)	(1,825)	(10,750)	(3,601)
Interest charges:
AFUDC	3,914	3,570	7,557	6,920
Interest expense	(62,464)	(59,935)	(123,178)	(120,085)
Income (loss) before income taxes	17,036	(5,998)	141,622	160,134
Income tax (benefit) expense	1,999	2,327	15,264	21,157
Net income (loss)	$ 15,037	$ (8,325)	$ 126,358	$ 138,977