Statements Of Operations - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Operating revenues	$ 174,363	$ 175,713	$ 902,253	$ 921,175
Operating expenses:
Fuel and purchased power	48,326	52,188	225,247	246,660
Operations and maintenance	80,413	80,160	335,136	321,254
Depreciation and amortization	25,126	23,814	97,694	92,723
Taxes other than income taxes	16,189	15,507	71,682	70,640
Utilities operating expense	170,054	171,669	729,759	731,277
Operating income	4,309	4,044	172,494	189,898
Other income (deductions):
Allowance for equity funds used during construction	1,001	920	3,534	3,130
Investment and interest income, net	23,707	5,155	36,929	34,745
Miscellaneous non-operating income	3,048	3,136	12,735	12,292
Miscellaneous non-operating deductions	(2,357)	(2,743)	(11,594)	(11,494)
Nonoperating income	25,399	6,468	41,604	38,673
Interest charges (credits):
Interest on long-term debt and revolving credit facility	18,989	17,988	76,425	72,591
Other interest	5,233	4,654	18,469	18,479
Capitalized interest	(1,532)	(1,214)	(5,801)	(4,942)
Allowance for borrowed funds used during construction	(972)	(898)	(3,686)	(3,082)
Interest expense	21,718	20,530	85,407	83,046
Income (loss) before income taxes	7,990	(10,018)	128,691	145,525
Income tax expense (benefit)	1,901	(3,052)	31,321	50,240
Net income (loss)	$ 6,089	$ (6,966)	$ 97,370	$ 95,285
Basic earnings (loss) per share	$ 0.15	$ (0.170)	$ 2.39	$ 2.35
Diluted earnings (loss) per share	0.15	(0.170)	2.39	2.34
Dividends declared per share of common stock	$ 0.360	$ 0.335	$ 1.440	$ 1.340
Weighted average number of shares outstanding	40,582,936	40,491,194	40,543,986	40,440,189
Weighted average number of shares and dilutive potential shares outstanding	40,663,753	40,491,194	40,661,228	40,563,625