Regulatory Matters (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($) item
Regulatory Assets:
Regulatory assets, current	$ 7,145	$ 7,052
Regulatory assets, long-term	209,934	209,708
Total Regulatory Assets	217,079	216,760
Regulatory Liabilities:
Regulatory liabilities, current	10,154	8,615
Regulatory liabilities, long-term	134,401	132,457
Total Regulatory Liabilities	144,555	141,072
Over recovered fuel costs
Regulatory Liabilities:
Regulatory liabilities, current	6,789	5,280
Regulatory liabilities, long-term	3,168	2,300
System reliability - vegetation management
Regulatory Liabilities:
Regulatory liabilities, long-term	1,320	1,320
Current portion of long-term regulatory liabilities
Regulatory Liabilities:
Regulatory liabilities, current	3,365	3,335
Other
Regulatory Liabilities:
Regulatory liabilities, long-term	493	56
Costs of removal
Regulatory Liabilities:
Regulatory liabilities, long-term	95,673	94,193
SWPA payment for Ozark Beach lost generation
Regulatory Liabilities:
Regulatory liabilities, long-term	13,580	14,213
Income taxes
Regulatory Liabilities:
Regulatory liabilities, long-term	11,194	11,244
Deferred construction accounting costs - fuel
Regulatory Liabilities:
Regulatory liabilities, long-term	7,651	7,690
Unamortized gain on interest rate derivative
Regulatory Liabilities:
Regulatory liabilities, long-term	2,989	3,031
Pension and other postretirement benefits
Regulatory Liabilities:
Regulatory liabilities, long-term	1,698	1,745
Under recovered fuel costs
Regulatory Assets:
Regulatory assets, current	89	196
Current portion of long-term regulatory assets
Regulatory Assets:
Regulatory assets, current	7,056	6,856
Pension and other postretirement benefits
Regulatory Assets:
Regulatory assets, long-term	106,237	108,273
Income taxes
Regulatory Assets:
Regulatory assets, long-term	48,597	48,613
Deferred construction accounting costs
Regulatory Assets:
Regulatory assets, long-term	14,886	14,977
Unamortized loss on reacquired debt
Regulatory Assets:
Regulatory assets, long-term	9,563	9,731
System reliability - vegetation management
Regulatory Assets:
Regulatory assets, long-term	3,346	3,604
Storm costs
Regulatory Assets:
Regulatory assets, long-term	3,389	3,531
Asset retirement obligation.
Regulatory Assets:
Regulatory assets, long-term	8,644	7,722
Customer programs
Regulatory Assets:
Regulatory assets, long-term	6,112	5,942
Missouri solar initiative
Regulatory Assets:
Regulatory assets, long-term	$ 6,170	$ 3,504
Number of solar rebate applications processed | item	467	262
Other
Regulatory Assets:
Regulatory assets, long-term	$ 2,261	$ 2,892
Electric | Unsettled derivative losses- electric segment
Regulatory Assets:
Regulatory assets, long-term	$ 7,785	$ 7,775