REGULATORY MATTERS (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets:
Regulatory assets, current		$ 7,052	$ 10,752
Regulatory assets, long-term		209,708	209,717
Total Regulatory Assets		216,760	220,469
Regulatory Liabilities:
Regulatory liabilities, current		8,615	7,898
Regulatory liabilities, long-term		132,457	128,471
Total Regulatory Liabilities		141,072	136,369
Missouri 2015 Rate Case | Iatan2
Regulatory Assets and Liabilities
Amortizable life tracking mechanism	3 years
Amortizable life tracking mechanism related to vegetation	5 years
Over recovered fuel costs
Regulatory Liabilities:
Regulatory liabilities, current		5,280	4,227
System reliability - vegetation management
Regulatory Liabilities:
Regulatory liabilities, long-term		1,320
Current portion of long-term regulatory liabilities
Regulatory Liabilities:
Regulatory liabilities, current		3,335	3,671
Other
Regulatory Liabilities:
Regulatory liabilities, long-term		56
Costs of removal
Regulatory Liabilities:
Regulatory liabilities, long-term		94,193	90,527
SWPA payment for Ozark Beach lost generation
Regulatory Liabilities:
Regulatory liabilities, long-term		14,213	16,744
Income taxes
Regulatory Liabilities:
Regulatory liabilities, long-term		11,244	11,451
Deferred construction accounting costs - fuel
Regulatory Liabilities:
Regulatory liabilities, long-term		7,690	7,849
Unamortized gain on interest rate derivative
Regulatory Liabilities:
Regulatory liabilities, long-term		$ 3,031	3,201
Unamortized gain on interest rate derivative | High end of range
Regulatory Liabilities:
Regulatory Asset Noncurrent, Amortization Period		25 years
Unamortized gain on interest rate derivative | Low end of range
Regulatory Liabilities:
Regulatory Asset Noncurrent, Amortization Period		4 years
Pension and other postretirement benefits
Regulatory Liabilities:
Regulatory liabilities, long-term		$ 1,745	2,369
Over recovered electric fuel and purchased power costs
Regulatory Liabilities:
Regulatory liabilities, long-term		2,300	1
Under recovered fuel costs
Regulatory Assets:
Regulatory assets, current		196	2,618
Total Regulatory Assets		5,900	3,100
Current portion of long-term regulatory assets
Regulatory Assets:
Regulatory assets, current		6,856	8,134
Pension and other postretirement benefits
Regulatory Assets:
Regulatory assets, long-term		$ 108,273	111,121
Regulatory Liabilities:
Regulatory Asset Noncurrent, Amortization Period		5 years
Portion of regulatory assets expected to be recoverable in future periods		$ 99,000
Income taxes
Regulatory Assets:
Regulatory assets, long-term		48,613	47,177
Deferred construction accounting costs
Regulatory Assets:
Regulatory assets, long-term		14,977	15,521
Unamortized loss on reacquired debt
Regulatory Assets:
Regulatory assets, long-term		$ 9,731	10,405
Unamortized loss on reacquired debt | High end of range
Regulatory Liabilities:
Regulatory Asset Noncurrent, Amortization Period		25 years
Unamortized loss on reacquired debt | Low end of range
Regulatory Liabilities:
Regulatory Asset Noncurrent, Amortization Period		4 years
System reliability - vegetation management
Regulatory Assets:
Regulatory assets, long-term		$ 3,604	5,337
Storm costs
Regulatory Assets:
Regulatory assets, long-term		$ 3,531	4,183
Regulatory Liabilities:
Regulatory Asset Noncurrent, Amortization Period		5 years
Asset retirement obligation.
Regulatory Assets:
Regulatory assets, long-term		$ 7,722	5,145
Total Regulatory Assets		7,700	5,100
Customer programs
Regulatory Assets:
Regulatory assets, long-term		5,942	5,253
Missouri solar initiative
Regulatory Assets:
Regulatory assets, long-term		3,504
Other
Regulatory Assets:
Regulatory assets, long-term		2,892	4,672
Ice storm and tornado cost
Regulatory Assets:
Regulatory assets, long-term		$ 2,900
Asbury five-year maintenance
Regulatory Liabilities:
Regulatory Asset Noncurrent, Amortization Period		5 years
Electric | Costs of removal
Regulatory Liabilities:
Total Regulatory Liabilities		$ 85,400	82,800
Electric | Unsettled derivative losses- electric segment
Regulatory Assets:
Regulatory assets, long-term		7,775	9,037
Gas | Costs of removal
Regulatory Liabilities:
Total Regulatory Liabilities		$ 8,800	$ 7,700