REGULATORY MATTERS (Details) (USD $)	12 Months Ended															12 Months Ended								12 Months Ended				12 Months Ended					12 Months Ended				12 Months Ended					12 Months Ended																			1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Regulated	Dec. 31, 2010 Regulated	Dec. 31, 2009 Regulated	Dec. 31, 2011 Missouri jurisdictional portion of the payment, net of tax	Dec. 31, 2011 Over recovered electric fuel and purchased power costs	Dec. 31, 2010 Over recovered electric fuel and purchased power costs	Dec. 31, 2011 Cost of removal	Dec. 31, 2010 Cost of removal	Dec. 31, 2011 Income taxes	Dec. 31, 2010 Income taxes	Dec. 31, 2011 Unamortized gain on interest rate derivative	Dec. 31, 2010 Unamortized gain on interest rate derivative	Dec. 31, 2011 Unamortized gain on interest rate derivative Minimum Y	Dec. 31, 2011 Unamortized gain on interest rate derivative Maximum Y	Dec. 31, 2011 Pension and other postretirement benefits	Dec. 31, 2010 Pension and other postretirement benefits	Dec. 31, 2011 Deferred construction accounting costs - fuel	Dec. 31, 2010 Deferred construction accounting costs - fuel	Dec. 31, 2010 Other	Dec. 31, 2011 SWPA payment for Ozark Beach lost generation	Dec. 31, 2011 SWPA payment for Ozark Beach lost generation Arkansas Y	Dec. 31, 2011 SWPA payment for Ozark Beach lost generation Missouri, Kansas and Oklahoma Y	Dec. 31, 2011 Under recovered electric fuel and purchased power costs	Dec. 31, 2010 Under recovered electric fuel and purchased power costs	Dec. 31, 2011 Under recovered electric fuel and purchased power costs Missouri M	Dec. 31, 2011 Pension and other postretirement benefits Y	Dec. 31, 2010 Pension and other postretirement benefits	Dec. 31, 2011 Income taxes	Dec. 31, 2010 Income taxes	Dec. 31, 2011 Storm costs Y	Dec. 31, 2010 Storm costs	Dec. 31, 2011 Unamortized loss on reacquired debt	Dec. 31, 2010 Unamortized loss on reacquired debt	Dec. 31, 2011 Unamortized loss on reacquired debt Minimum Y	Dec. 31, 2011 Unamortized loss on reacquired debt Maximum Y	Dec. 31, 2011 Deferred operating and maintenance expenses	Dec. 31, 2011 Unamortized loss on interest rate derivative	Dec. 31, 2010 Unamortized loss on interest rate derivative	Dec. 31, 2011 Unamortized loss on interest rate derivative Minimum Y	Dec. 31, 2011 Unamortized loss on interest rate derivative Maximum Y	Dec. 31, 2011 Asbury five-year maintenance Y	Dec. 31, 2010 Asbury five-year maintenance	Dec. 31, 2011 Deferred construction accounting costs.	Dec. 31, 2010 Deferred construction accounting costs.	Dec. 31, 2011 Asset retirement obligation:	Dec. 31, 2010 Asset retirement obligation:	Dec. 31, 2011 Customer programs	Dec. 31, 2010 Customer programs	Dec. 31, 2011 System reliability - vegetation management	Dec. 31, 2010 System reliability - vegetation management	Dec. 31, 2011 Other:	Dec. 31, 2010 Other:	Dec. 31, 2010 Gas	Dec. 31, 2011 Gas Cost of removal	Dec. 31, 2010 Gas Cost of removal	Dec. 31, 2011 Gas Under recovered purchased gas costs	Dec. 31, 2010 Gas Under recovered purchased gas costs	Jan. 31, 2012 Electric Kansas 2009 Rate Case Kansas Corporation Commission (KCC) Y	Dec. 31, 2011 Electric Cost of removal	Dec. 31, 2010 Electric Cost of removal	Dec. 31, 2011 Electric Unsettled derivative losses	Dec. 31, 2010 Electric Unsettled derivative losses	Dec. 31, 2011 Iatan2	Dec. 31, 2010 Iatan2
Regulatory Assets and Liabilities
Deferred depreciation, operations and maintenance, and carrying costs related to capital expenditure							$ 1,600,000
Period over which deferred depreciation, operating and maintenance expenses will be recovered (in years)																																																													4
Deferred construction accounting costs	17,095,000	10,521,000																																																																10,890,000	4,524,000
Deferred fuel and purchased power expense																																																																		8,300,000
Regulatory Assets:
Regulatory assets, current	7,724,000	4,974,000																								7,513,000	4,974,000																																211,000
Regulatory assets, long-term	231,922,000	189,404,000																								231,000			121,058,000	92,192,000	49,631,000	50,188,000	5,303,000	7,733,000	11,610,000	13,099,000			952,000	1,462,000	1,776,000			492,000	948,000	17,095,000	10,521,000	3,571,000	3,412,000	3,408,000	2,119,000	6,569,000	3,338,000	1,420,000	473,000				1,281,000	439,000				7,839,000	3,166,000
Regulatory assets, total	239,646,000	194,378,000																																														3,600,000	3,400,000
Regulatory Asset Noncurrent, Amortization Period (in years)																													5				5				2	30				2	30	5
Amortization period (in years)																								50	10
Period to recover costs in Missouri rates (in months)																												12
Pension and other postretirement benefit costs recognized																													500,000
Portion of regulatory assets expected to be recoverable in future periods																													113,800,000
Regulatory Liabilities:
Regulatory liabilities, current		1,243,000																																																						1,243,000
Regulatory liabilities, long-term	128,440,000	87,579,000						2,513,000	409,000	73,562,000	62,756,000	12,337,000	12,715,000	3,711,000	3,881,000			2,939,000	4,604,000	8,304,000	3,126,000	88,000	25,074,000
Regulatory liabilities, total	128,440,000	88,822,000																																																							5,000,000	3,900,000				68,600,000	58,800,000
Period over which gain (loss) on interst rate derivative amortized																2	30
Pension and other postretirement benefit costs reduction recognized																													500,000
Amortization	$ 7,445,000	$ 8,347,000	$ 5,159,000	$ 6,600,000	$ 7,500,000	$ 4,500,000