STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating revenues	$ 903,603	$ 916,797	$ 886,936
Operating expenses:
Fuel and purchased power	229,109	244,751	233,465
Operations and maintenance	334,883	320,281	315,710
Depreciation and amortization	96,382	90,843	84,317
Taxes other than income taxes	71,000	70,863	65,533
Utilities operating expense	731,374	726,738	699,025
Operating income	172,229	190,059	187,911
Other income (deductions):
Allowance for equity funds used during construction	3,453	3,025	7,023
Investment and interest income, net	18,377	38,853	34,797
Miscellaneous non-operating income	12,823	12,051	11,073
Miscellaneous non-operating deductions	(11,980)	(11,580)	(11,038)
Nonoperating income	22,673	42,349	41,855
Interest charges (credits):
Interest on long-term debt and revolving credit facility	75,424	72,970	71,544
Other interest	17,890	18,170	17,509
Capitalized interest	(5,483)	(5,022)	(4,990)
Allowance for borrowed funds used during construction	(3,612)	(2,975)	(4,983)
Interest expense	84,219	83,143	79,080
Income before income taxes	110,683	149,265	150,686
Income tax expense	26,368	51,004	53,918
Net income	$ 84,315	$ 98,261	$ 96,768
Basic earnings per share	$ 2.070	$ 2.420	$ 2.390
Diluted earnings per share	2.070	2.420	2.390
Dividends declared per share of common stock	$ 1.415	$ 1.315	$ 1.225
Weighted average number of shares outstanding	40,521,364	40,414,556	40,350,688
Weighted average number of shares and dilutive potential shares outstanding	40,642,640	40,535,191	40,408,033