SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 3)			12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($) item	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($)	Oct. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Asset Retirement Obligation
Proportionate ownership interest (as a percent)						12.00%
Change in asset retirement obligation
Asset retirement obligation	$ 15,072,000	$ 4,847,000	$ 4,847,000	$ 4,190,000	$ 4,190,000	$ 15,072,000		$ 4,847,000
Opening balance of asset retirement obligation			4,847,000	4,190,000
Liabilities Recognized			9,812,000
Liabilities settled			(73,000)	(1,175,000)
Accretion			486,000	172,000
Cash Flow Revisions				1,660,000
Closing balance of asset retirement obligation	15,072,000	4,847,000	$ 15,072,000	$ 4,847,000	$ 4,190,000
Regulatory assets						216,760,000		220,469,000
Allowance for Funds Used During Construction
Aggregate rates (on a before-tax basis)			5.50%	6.60%	7.30%
Asset Impairments (excluding goodwill)
Assets impaired	0	$ 0
Goodwill
Number of assumptions whose negative charge will affect impairment | item			1
Number of approaches used to estimate the fair value | item			2
Fuel and Purchased Power
Inventory allowances						0
Pension and Other Postretirement Benefits
Percentage that unrecognized gains or losses must exceed postretirement benefit obligation or fair value of plan assets for recognition of additional income or expense			10.00%
Amortization period of unrecognized gains or losses into actuarial expense			10 years
Cash & Cash Equivalents
Checks and electronic fund transfers that have been issued but not cleared through bank						23,200,000		28,300,000
Restricted Cash
Amounts restricted for operating costs						1,800,000		1,800,000
Asbury Power Plant
Change in asset retirement obligation
Asset retirement obligation	5,400,000		$ 5,400,000			5,400,000
Closing balance of asset retirement obligation	5,400,000		5,400,000
Iatan Generating Station
Change in asset retirement obligation
Asset retirement obligation	4,400,000		4,400,000			4,400,000
Closing balance of asset retirement obligation	$ 4,400,000		$ 4,400,000
SPP
Restricted Cash
Amounts restricted for secured collateral						2,500,000		2,500,000
MISO
Restricted Cash
Amounts restricted for secured collateral						$ 500,000		500,000
Electric
Fuel and Purchased Power
Number of NOx annual allowances purchased for compliance | item				69
Electric | Missouri Public Service Commission (MPSC)
Fuel and Purchased Power
Percentage of changes in fuel and purchased power costs from the base cost permitted for distribution to customers under fuel adjustment clause			95.00%
Gas
Fuel and Purchased Power
Maximum number of rate changes allowed by PGA clause throughout the year | item			4
Low end of range
Asset Retirement Obligation
Credit adjusted risk-free rate (as a percent)						4.50%
Low end of range | Gas
Goodwill
Excess fair value of the reporting unit over carrying value							$ 18,000,000
High end of range
Asset Retirement Obligation
Credit adjusted risk-free rate (as a percent)						5.52%
High end of range | Gas
Goodwill
Excess fair value of the reporting unit over carrying value							$ 22,000,000
Asset retirement obligation.
Change in asset retirement obligation
Regulatory assets						$ 7,700,000		5,100,000
Under recovered fuel costs
Change in asset retirement obligation
Regulatory assets						5,900,000		3,100,000
Acid Rain SO2
Fuel and Purchased Power
Inventory allowances						11,443		$ 872
CSAPR SO2
Fuel and Purchased Power
Inventory allowances						5,861
CSAPR NOx (annual)
Fuel and Purchased Power
Inventory allowances						500
CSAPR Nox (seasonal)
Fuel and Purchased Power
Inventory allowances						$ 241