STATEMENTS OF OPERATIONS (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating revenues	$ 890,362	$ 852,881	$ 918,013
Energy expenses:
Fuel	226,768	191,076	223,507
Purchased and interchanged power	62,363	60,251	75,149
Cost of services, energy services	289,131	251,327	298,656
Operating revenues net of energy expenses	601,231	601,554	619,357
Other operating expenses:
Other operations	237,155	236,558	229,570
Maintenance	61,068	60,339	62,092
Depreciation and amortization	79,626	78,556	81,331
Taxes other than income taxes	57,747	57,443	55,561
Utilities operating expense	435,596	432,896	428,554
Operating income	165,635	168,658	190,803
Other income (deductions):
Allowance for equity funds used during construction	10,008	9,427	8,161
Investment and interest income, net	7,033	5,275	5,664
Miscellaneous non-operating income	909	1,415	885
Miscellaneous non-operating deductions	(3,635)	(2,013)	(3,187)
Nonoperating income (expense)	14,315	14,104	11,523
Interest charges (credits):
Interest on long-term debt and revolving credit facility	58,635	54,632	54,115
Other interest	431	1,190	989
Capitalized interest	(5,299)	(5,312)	(5,177)
Allowance for borrowed funds used during construction	(6,055)	(5,573)	(4,848)
Interest expense	47,712	44,937	45,079
Income before income taxes	132,238	137,825	157,247
Income tax expense	43,655	46,979	53,708
Net income	$ 88,583	$ 90,846	$ 103,539
Basic earnings per share	$ 2.200	$ 2.270	$ 2.490
Diluted earnings per share	$ 2.200	$ 2.260	$ 2.480
Dividends declared per share of common stock	$ 1.045	$ 0.970	$ 0.660
Weighted average number of shares outstanding	40,114,594	39,974,022	41,349,883
Weighted average number of shares and dilutive potential shares outstanding	40,126,647	40,055,581	41,587,059