Regulatory Matters (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) item	Dec. 31, 2014 USD ($)
Regulatory Assets:
Regulatory assets, current	$ 7,306	$ 10,752
Regulatory assets, long-term	202,139	209,717
Total Regulatory Assets	209,445	220,469
Regulatory Liabilities:
Regulatory liabilities, current	6,356	7,898
Regulatory liabilities, long-term	136,165	128,471
Total Regulatory Liabilities	142,521	136,369
Over recovered fuel costs
Regulatory Liabilities:
Regulatory liabilities, current	2,934	4,227
Regulatory liabilities, long-term	5,512	1
Current portion of long-term regulatory liabilities
Regulatory Liabilities:
Regulatory liabilities, current	3,422	3,671
Costs of removal
Regulatory Liabilities:
Regulatory liabilities, long-term	94,503	90,527
SWPA payment for Ozark Beach lost generation
Regulatory Liabilities:
Regulatory liabilities, long-term	14,793	16,744
Income taxes
Regulatory Liabilities:
Regulatory liabilities, long-term	11,291	11,451
Deferred construction accounting costs - fuel
Regulatory Liabilities:
Regulatory liabilities, long-term	7,730	7,849
Unamortized gain on interest rate derivative
Regulatory Liabilities:
Regulatory liabilities, long-term	3,074	3,201
Pension and other postretirement benefits
Regulatory Liabilities:
Regulatory liabilities, long-term	1,364	2,369
Under recovered fuel costs
Regulatory Assets:
Regulatory assets, current	159	2,618
Regulatory assets, long-term	1,744	951
Current portion of long-term regulatory assets
Regulatory Assets:
Regulatory assets, current	7,147	8,134
Pension and other postretirement benefits
Regulatory Assets:
Regulatory assets, long-term	102,844	111,121
Income taxes
Regulatory Assets:
Regulatory assets, long-term	48,253	47,177
Deferred construction accounting costs
Regulatory Assets:
Regulatory assets, long-term	15,114	15,521
Unamortized loss on reacquired debt
Regulatory Assets:
Regulatory assets, long-term	9,900	10,405
System reliability - vegetation management
Regulatory Assets:
Regulatory assets, long-term	3,863	5,337
Regulatory Liabilities:
Regulatory liabilities, long-term	1,320
Storm costs
Regulatory Assets:
Regulatory assets, long-term	3,672	4,183
Asset retirement obligation.
Regulatory Assets:
Regulatory assets, long-term	6,800	5,145
Customer programs
Regulatory Assets:
Regulatory assets, long-term	5,820	5,253
Missouri solar initiative
Regulatory Assets:
Regulatory assets, long-term	$ 1,719
Number of solar rebate applications processed | item	109
Rebate Commitments	$ 1,600
Other
Regulatory Assets:
Regulatory assets, long-term	2,993	3,721
Ice storm and tornado cost
Regulatory Assets:
Regulatory assets, long-term	3,000
Electric | Unsettled derivative losses- electric segment
Regulatory Assets:
Regulatory assets, long-term	$ 6,564	$ 9,037