Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
STATEMENT OF COMPREHENSIVE INCOME
Operating Revenues	$ 437,835	$ 434,484	$ 421,817
OPERATING EXPENSES:
General and administrative	68,473	55,735	54,067
Operation and maintenance	75,371	72,701	68,611
Depreciation	93,419	90,486	87,915
Regulatory credits	(494)	(1,023)	(1,662)
Taxes, other than income taxes	19,484	19,356	18,106
Total operating expenses	256,253	237,255	227,037
Operating Income	181,582	197,229	194,780
OTHER (INCOME) AND OTHER DEDUCTIONS:
Interest on long-term debt	44,439	44,439	44,458
Other interest	1,918	1,994	2,664
Allowance for equity and borrowed funds used during construction	(2,291)	(2,101)	(2,824)
Miscellaneous other (income) deductions, net	793	84	955
Total other (income) and other deductions	44,859	44,416	45,253
NET INCOME	136,723	152,813	149,527
CASH FLOW HEDGES:
Amortization of cash flow hedges	(62)	(62)	(62)
COMPREHENSIVE INCOME	$ 136,661	$ 152,751	$ 149,465