STATEMENTS OF INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
STATEMENTS OF INCOME (UNAUDITED) [Abstract]
Operating revenues	$ 340,488	$ 381,209
Operating expenses
Electric fuel and purchased power	203,261	249,250
Operating and maintenance expenses	63,140	62,753
Demand side management program expenses	3,077	3,429
Depreciation and amortization	27,846	26,158
Taxes (other than income taxes)	11,319	10,120
Total operating expenses	308,643	351,710
Operating income	31,845	29,499
Other (expense) income, net	(122)	62
Allowance for funds used during construction - equity	1,690	1,926
Interest charges and financing costs
Interest charges - includes other financing costs of $768 and $660, respectively	16,706	15,798
Allowance for funds used during construction - debt	(1,083)	(1,349)
Total interest charges and financing costs	15,623	14,449
Income before income taxes	17,790	17,038
Income taxes	6,430	6,800
Net income	$ 11,360	$ 10,238