CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues
Electric	$ 805,554	$ 797,562	$ 790,701
Gas	263,394	318,335	318,735
Other	1,394	1,419	1,284
Total Revenues	1,070,342	1,117,316	1,110,720
Operating Expenses
Cost of sales	395,434	494,559	531,089
Operating, general and administrative	269,966	267,160	237,047
Mountain States Transmission Intertie impairment	24,039	0	0
Property and other taxes	97,674	89,122	88,198
Depreciation	106,044	100,926	91,769
Total Operating Expenses	893,157	951,767	948,103
Operating Income	177,185	165,549	162,617
Interest Expense	(65,062)	(66,859)	(65,826)
Other Income	4,372	3,931	6,345
Income Before Income Taxes	116,495	102,621	103,136
Income Tax Expense	(18,089)	(10,065)	(25,760)
Net Income	$ 98,406	$ 92,556	$ 77,376
Average Common Shares Outstanding	36,847,427	36,258,463	36,190,373
Basic Earnings per Average Common Share	$ 2.67	$ 2.55	$ 2.14
Diluted Earnings per Average Common Share	$ 2.66	$ 2.53	$ 2.14
Dividends Declared per Average Common Share	$ 1.48	$ 1.44	$ 1.36