Regulatory Matters (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($) item	Dec. 31, 2015 USD ($) item
Regulatory Assets:
Regulatory assets, current	$ 7,120	$ 7,052
Regulatory assets, long-term	209,682	209,708
Total Regulatory Assets	216,802	216,760
Regulatory Liabilities:
Regulatory liabilities, current	12,290	8,615
Regulatory liabilities, long-term	142,017	132,457
Total Regulatory Liabilities	154,307	141,072
Over recovered fuel costs
Regulatory Liabilities:
Regulatory liabilities, current	9,032	5,280
Regulatory liabilities, long-term	8,950	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	3,258	3,335
Other
Regulatory Liabilities:
Regulatory liabilities, long-term	409	56
Costs of removal
Regulatory Liabilities:
Regulatory liabilities, long-term	98,132	94,193
SWPA payment for Ozark Beach lost generation
Regulatory Liabilities:
Regulatory liabilities, long-term	13,001	14,213
Income taxes
Regulatory Liabilities:
Regulatory liabilities, long-term	11,165	11,244
Deferred construction accounting costs - fuel
Regulatory Liabilities:
Regulatory liabilities, long-term	7,613	7,690
Unamortized gain on interest rate derivative
Regulatory Liabilities:
Regulatory liabilities, long-term	2,946	3,031
Pension and other postretirement benefits
Regulatory Liabilities:
Regulatory liabilities, long-term	1,739	1,745
Under recovered fuel costs
Regulatory Assets:
Regulatory assets, current	72	196
Current portion of long-term regulatory assets
Regulatory Assets:
Regulatory assets, current	7,048	6,856
Pension and other postretirement benefits
Regulatory Assets:
Regulatory assets, long-term	104,328	108,273
Income taxes
Regulatory Assets:
Regulatory assets, long-term	48,546	48,613
Deferred construction accounting costs
Regulatory Assets:
Regulatory assets, long-term	14,799	14,977
Unamortized loss on reacquired debt
Regulatory Assets:
Regulatory assets, long-term	9,394	9,731
System reliability - vegetation management
Regulatory Assets:
Regulatory assets, long-term	3,088	3,604
Storm costs
Regulatory Assets:
Regulatory assets, long-term	3,253	3,531
Asset retirement obligation.
Regulatory Assets:
Regulatory assets, long-term	9,568	7,722
Customer programs
Regulatory Assets:
Regulatory assets, long-term	6,698	5,942
Missouri solar initiative
Regulatory Assets:
Regulatory assets, long-term	$ 10,336	$ 3,504
Number of solar rebate applications processed | item	748	262
Other
Regulatory Assets:
Regulatory assets, long-term	$ 2,195	$ 2,892
Electric | Unsettled derivative losses- electric segment
Regulatory Assets:
Regulatory assets, long-term	$ 4,525	$ 7,775