Statement of Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Statement of Income [Abstract]
OPERATING REVENUES	$ 434,484	$ 421,817	$ 434,379
OPERATING EXPENSES:
General and administrative	59,253	57,162	64,657
Operation and maintenance	69,183	65,516	71,085
Depreciation	90,486	87,915	86,373
Regulatory credits	(1,023)	(1,662)	(2,403)
Taxes, other than income taxes	19,356	18,106	14,158
Total operating expenses	237,255	227,037	233,870
Operating Income	197,229	194,780	200,509
Interest income -
Affiliated	8	27	74
Other	16	3	16
Allowance for equity funds used during construction	1,438	1,947	1,996
Miscellaneous other expense, net	(108)	(985)	(135)
Total other income - net	1,354	992	1,951
INTEREST CHARGES:
Interest on long-term debt	44,439	44,458	44,439
Other interest	1,994	2,664	5,414
Allowance for borrowed funds used during construction	(663)	(877)	(1,044)
Total interest charges	45,770	46,245	48,809
NET INCOME	$ 152,813	$ 149,527	$ 153,651