COMMITMENTS AND CONTINGENCIES (Details) (USD $)	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended		21 Months Ended				12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended
	Aug. 31, 2010 phase	Dec. 31, 2012 plaintiff MW	Dec. 31, 2004 Elk River Windfarm	Dec. 31, 2012 Elk River Windfarm MW	Dec. 31, 2012 Southern Star Central Pipeline, Inc. Electric	Dec. 31, 2012 Southern Star Central Pipeline, Inc. Electric Dth	Dec. 31, 2012 Iatan	Dec. 31, 2012 Physical gas and transportation contracts	Dec. 31, 2012 Coal and coal transportation contracts	Dec. 31, 2012 Purchased power Plum Point Energy Station MW	Dec. 31, 2008 Purchased power Cloud County Windfarm	Dec. 31, 2012 Purchased power Cloud County Windfarm MW	Dec. 31, 2005 Purchased power Elk River Windfarm	Dec. 31, 2012 Purchased power Elk River Windfarm	Dec. 31, 2012 Leases	Dec. 31, 2011 Leases	Dec. 31, 2010 Leases	Dec. 31, 2012 Leases Electric train	Dec. 31, 2012 Leases Gas office	Dec. 31, 2012 Leases Plum Point Energy Station railcar
Commitments and Contingencies
Proportionate ownership interest (as a percent)		12.00%					12.00%
January 1, 2013 through December 31, 2014								$ 29,400,000	$ 23,600,000
January 1, 2015 through December 31, 2016								29,900,000	32,100,000
January 1, 2017 through December 31, 2018								22,200,000	22,700,000
January 1, 2019 and beyond								8,300,000	22,700,000
Term of long-term contract agreement			20 years			5 years				30 years	20 years
Agreement to purchase firm gas storage capacity (in Dths)						1,000,000
Amount of annual storage capacity reservation					1,100,000
Amount of long-term contract obligation										306,700,000
Energy capacity owned (in megawatts)				150						670		105
Amount of energy capacity owned (in megawatts)										50
Amount of energy capacity under option to purchase (in megawatts)										50
Amount of total power capacity of generating facility (in megawatts)		18
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											20 years		20 years
Number of phases approved under the capital reliability rider preceding a general rate case	2
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, 2013															595,000
Capital leases, 2014															553,000
Capital leases, 2015															553,000
Capital leases, 2016															549,000
Capital leases, 2017															546,000
Capital leases, thereafter															4,100,000
Capital leases, total minimum payments															6,896,000
Capital leases, amount representing interest															2,157,000
Capital leases, present value of net minimum lease payments															4,739,000
Operating leases, 2013															788,000
Operating leases, 2014															732,000
Operating leases, 2015															726,000
Operating leases, 2016															721,000
Operating leases, 2017															682,000
Operating leases, thereafter															1,131,000
Operating leases, total minimum payments															4,780,000
Expenses incurred related to operating leases															900,000	1,000,000	800,000
Accumulated amount of amortization of capital leases															$ 1,000,000	$ 1,000,000
Number of plaintiffs		3