Commitments and Contingencies (Details) (USD $)	9 Months Ended												9 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Physical gas and transportation contracts	Sep. 30, 2011 Coal and coal transportation contracts	Sep. 30, 2011 New construction megawatt	Jun. 15, 2011 New construction Missouri Public Service Commission (MPSC)	May 27, 2011 New construction Missouri Public Service Commission (MPSC)	Sep. 28, 2010 New construction Missouri Public Service Commission (MPSC)	Feb. 02, 2011 New construction Arkansas Public Service Commission (APSC)	Aug. 19, 2010 New construction Arkansas Public Service Commission (APSC)	Jun. 30, 2011 New construction Oklahoma Corporation Commission (OCC)	Aug. 30, 2010 New construction Oklahoma Corporation Commission (OCC)	Sep. 30, 2011 New construction Kansas Corporation Commission (KCC) Y	Jun. 17, 2011 New construction Kansas Corporation Commission (KCC)	May 04, 2010 New construction Kansas Corporation Commission (KCC)	Sep. 30, 2011 Leases Facility train	Sep. 30, 2011 Leases Plum Point Energy Station railcar	Sep. 30, 2011 Plum Point Energy Station megawatt	Sep. 30, 2011 Cloud County Windfarm megawatt	Sep. 30, 2011 Elk River Windfarm megawatt	Sep. 30, 2011 Southern Star Central Pipeline, Inc. Dth	Sep. 30, 2011 Federal Energy Regulatory Commission (FERC) GFR rate case	Jun. 30, 2010 Federal Energy Regulatory Commission (FERC) GFR rate case customer
Commitments and Contingencies
Percentage of ownership interest in Iatan generating facility (as a percent)	12.00%
Number of on-system wholesale customers who were granted intervention																							3
Accumulated provision - rate refunds																						$ 1,200,000
Accumulated provision - rate refunds	603,000	271,000
October 1, 2011 through December 31, 2011			10,400,000	8,600,000
January 1, 2012 through December 31, 2013			56,900,000	56,600,000
January 1, 2014 through December 31, 2015			29,400,000	36,400,000
January 1, 2016 and beyond			25,800,000	15,700,000
Agreement to purchase firm gas storage capacity (in Dths)																					1,000,000
Term of long-term contract agreement (in years)																		30 year	20 year	20 year	five years
Amount of annual storage capacity reservation																					1,100,000
Amount of energy generated (in megawatts)																		665	105	150
Amount of energy capacity under option to purchase (in megawatts)																		50
Amount of long-term contract obligation																		37,300,000
Ownership interest in the Iatan 2 generating facility (as a percent)					12.00%
Ownership interest in the Iatan 2 generating facility (in megawatts)					102
Amount of total power capacity of Iatan 2 generating facility (in megawatts)					850
Company's share of Iatan 2 generating facility construction costs (low end of the range)					237,000,000
Company's expected share of Iatan 2 generating facility construction costs (high end of the range)					240,000,000
Company's share of Iatan 2 generating facility construction costs incurred through the period					232,600,000
Amount of allowance for funds used during construction (AFUDC)					19,100,000
Requested amount of annual increase in electric base rate								36,500,000		3,200,000	600,000			1,500,000
Percentage of annual electric base rate increase requested (as a percent)								9.20%		27.30%	4.10%			6.39%
Regulatory amortization expense						14,500,000
Annual amount of electric base rate increase approved												2,600,000
Percentage of annual electric base rate increase approved (as a percent)												27.67%
Approved amount of annual increase in electric base rate							18,700,000								2,800,000
Approved percentage of annual increase in electric base rate (as a percent)							4.70%								12.40%
Period over which deferred depreciation, operating and maintenance expenses will be recovered (in years)													3
General rate increase amount as per the unanimous settlement									$ 2,100,000
Percentage of generate rate increase in electric base rate (as a percent)									19.00%
Number of unit trains under short-term operating leases																2
Number of gas segment offices under operating lease																1
Number of railcars under capital leases																	108