COMMITMENTS AND CONTINGENCIES (Details) (USD $)	12 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended		12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended		70 Months Ended	12 Months Ended
	Dec. 31, 2011 plaintiff	Dec. 31, 2009 MW	Dec. 31, 2011 Missouri Public Service Commission (MPSC) decision	Dec. 31, 2004 Elk River Windfarm Y	Dec. 31, 2011 Elk River Windfarm MW	Dec. 31, 2011 Southern Star Central Pipeline, Inc. Electric dth	Dec. 31, 2011 Southern Star Central Pipeline, Inc. Electric	Dec. 31, 2011 Iatan	Dec. 31, 2011 Physical gas and transportation contracts	Dec. 31, 2011 Coal and coal transportation contracts Y	Dec. 31, 2011 Purchased power Plum Point Energy Station MW Y	Dec. 31, 2008 Purchased power Cloud County Windfarm Y	Dec. 31, 2011 Purchased power Cloud County Windfarm MW	Dec. 31, 2011 Purchased power Elk River Windfarm Y	Feb. 02, 2011 New construction Arkansas Public Service Commission (APSC)	Aug. 31, 2010 New construction Oklahoma Corporation Commission (OCC) phase	Mar. 31, 2006 New construction Plum point MW	Dec. 31, 2011 New construction Plum point	Dec. 31, 2011 New construction Iatan2 MW	Dec. 31, 2011 Leases	Dec. 31, 2010 Leases	Dec. 31, 2009 Leases	Dec. 31, 2011 Leases Electric train	Dec. 31, 2011 Leases Gas office	Dec. 31, 2011 Leases Plum Point Energy Station railcar
Commitments and Contingencies
Proportionate ownership interest (as a percent)	12.00%							12.00%									7.52%		12.00%
Number of decisions pointed by plaintiffs			2
January 1, 2012 through December 31, 2012									$ 30,900,000	$ 35,300,000
January 1, 2013 through December 31, 2014									43,500,000	46,700,000
January 1, 2015 through December 31, 2016									24,500,000	31,300,000
January 1, 2017 and beyond									17,800,000
Term of long-term contract agreement (in years)				20						6.5	30	20
Agreement to purchase firm gas storage capacity (in Dths)						1,000,000
Term of long-term contract agreement (in years)						five years
Amount of annual storage capacity reservation							1,100,000
Amount of long-term contract obligation										91,900,000	35,000,000
Amount of energy generated (in megawatts)					150						665		105
Amount of energy capacity under option to purchase (in megawatts)											50
Maximum annual payments contingent upon output of the facility													14,600,000	16,900,000
Period of the average cost that is used as a basis for determining the maximum annual payments (in years)												20		20
Ownership interest in generating facility (in megawatts)																	50		102
Ownership interest in generating facility (as a percent)	12.00%							12.00%									7.52%		12.00%
Company's share of generating facility costs incurred through the period excluding AFUDC																		86,800,000	233,300,000
Amount of total power capacity of generating facility (in megawatts)		18																	850
Number of phases approved under the capital reliability rider preceding a general rate case																2
Percentage of generate rate increase in electric base rate															19.00%
Number of unit trains under short-term operating leases																							2
Number of office facilities under short-term operating leases																								1
Number of railcars under capital leases																									108
Gross amount of assets recorded under capital leases																				5,500,000
Capital leases, 2012																				618,000
Capital leases, 2013																				595,000
Capital leases, 2014																				553,000
Capital leases, 2015																				553,000
Capital leases, 2016																				549,000
Capital leases, thereafter																				4,646,000
Capital leases, total minimum payments																				7,514,000
Capital leases, amount representing interest																				2,483,000
Capital leases, present value of net minimum lease payments																				5,031,000
Operating leases, 2012																				939,000
Operating leases, 2013																				758,000
Operating leases, 2014																				720,000
Operating leases, 2015																				720,000
Operating leases, 2016																				720,000
Operating leases, thereafter																				1,813,000
Operating leases, total minimum payments																				5,670,000
Operating leases, present value of net minimum lease payments																				5,670,000
Expenses incurred related to operating leases																				1,000,000	800,000	1,400,000
Accumulated amount of amortization of capital leases																				1,000,000	600,000
Amount of allowance for funds used during construction (AFUDC)																		$ 16,500,000	$ 19,100,000
Number of plaintiffs	3