SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2011 Y	Dec. 31, 2010	Dec. 31, 2009	Sep. 07, 2010	Dec. 31, 2008
Fuel, Materials and Supplies
Total	$ 62,239,000	$ 45,557,000
Income taxes
Amortization period for unamortized investment tax credits (in years)	52
Advanced coal investment tax credit granted previously			125,000,000
Revised coal investment tax credit				17,700,000
Investment Tax Credit Utilized Maximum	200,000
Accounting for Uncertainty in Income Taxes
Unrecognized tax benefits	0	359,000	906,000		2,176,000
No material changes to unrecognized tax benefits in other expenses (in years)	12
Weighted Average Number Of Shares
Basic (in shares)	41,851,759	40,544,802	34,923,526
Dilutive Securities:
Performance-based restricted stock awards (in shares)	18,222	14,991	20,513
Dividend equivalents (in shares)	9,585	12,558	12,122
Employee stock purchase plan (in shares)	3,815	7,170	103
Stock options (in shares)	3,240
Time-based restricted stock awards	807
Total dilutive securities (in shares)	35,669	34,719	32,738
Diluted weighted average number of shares	41,887,428	40,579,521	34,956,264
Antidilutive Shares		74,800	117,178
Electric fuel inventory
Fuel, Materials and Supplies
Total	27,341,000	17,648,000
Natural gas inventory
Fuel, Materials and Supplies
Total	6,346,000	4,470,000
Materials and supplies
Fuel, Materials and Supplies
Total	$ 28,462,000	$ 23,439,000