STATEMENTS OF INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]
Operating Revenues	$ 446,480	$ 421,874	$ 412,449
Operating Expenses:
Cost of Sales (Excluding depreciation)	200,081	188,710	187,866
Operations	85,805	78,425	68,149
Maintenance	13,135	13,615	13,122
Depreciation	33,775	31,062	30,358
Energy and Other Taxes	7,862	8,300	10,291
Total Operating Expenses	340,658	320,112	309,786
Operating Income	105,822	101,762	102,663
Other Income and Expense	3,797	2,617	3,429
Interest Charges	(12,550)	(12,427)	(18,922)
Income Before Income Taxes	97,069	91,952	87,170
Income Taxes	(34,833)	(33,711)	(34,281)
Net Income	$ 62,236	$ 58,241	$ 52,889