CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating revenues
Electric	$ 881,891	$ 849,946	$ 834,998
Natural gas	122,353	106,157	120,147
Other	1,207	1,130	1,396
Total operating revenues	1,005,451	957,233	956,541
Operating expenses
Electric fuel and purchased power, non-affiliates	16,197	15,574	10,795
Purchased power, affiliates	421,609	413,615	419,028
Cost of natural gas sold and transported	62,259	54,436	70,988
Operating and maintenance expenses	205,539	194,927	179,413
Conservation program expenses	12,572	12,645	11,695
Depreciation and amortization	111,216	98,294	91,245
Taxes (other than income taxes)	27,831	27,814	28,181
Loss on Monticello life cycle management/extended power uprate project	0	0	5,237
Total operating expenses	857,223	817,305	816,582
Operating income	148,228	139,928	139,959
Other income, net	833	461	883
Allowance for funds used during construction — equity	6,707	4,277	7,253
Interest charges and financing costs
Interest charges — includes other financing costs of $1,855, $1,854, and $1,738, respectively	35,040	34,452	32,731
Allowance for funds used during construction - debt	(2,860)	(1,823)	(3,510)
Total interest charges and financing costs	32,180	32,629	29,221
Income before income taxes	123,588	112,037	118,874
Income taxes	44,172	42,902	44,238
Net income	$ 79,416	$ 69,135	$ 74,636