Regulatory Matters (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($) item	Dec. 31, 2014 USD ($)
Regulatory Assets:
Regulatory assets, current	$ 7,955	$ 10,752
Regulatory assets, long-term	202,134	209,717
Total Regulatory Assets	210,089	220,469
Regulatory Liabilities:
Regulatory liabilities, current	7,477	7,898
Regulatory liabilities, long-term	135,319	128,471
Total Regulatory Liabilities	142,796	136,369
Over recovered fuel costs
Regulatory Liabilities:
Regulatory liabilities, current	4,235	4,227
Regulatory liabilities, long-term	5,666	1
Current portion of long-term regulatory liabilities
Regulatory Liabilities:
Regulatory liabilities, current	3,242	3,671
Costs of removal
Regulatory Liabilities:
Regulatory liabilities, long-term	93,356	90,527
SWPA payment for Ozark Beach lost generation
Regulatory Liabilities:
Regulatory liabilities, long-term	15,485	16,744
Income taxes
Regulatory Liabilities:
Regulatory liabilities, long-term	11,382	11,451
Deferred construction accounting costs - fuel
Regulatory Liabilities:
Regulatory liabilities, long-term	7,769	7,849
Unamortized gain on interest rate derivative
Regulatory Liabilities:
Regulatory liabilities, long-term	3,116	3,201
Pension and other postretirement benefits
Regulatory Liabilities:
Regulatory liabilities, long-term	1,787	2,369
Under recovered fuel costs
Regulatory Assets:
Regulatory assets, current	253	2,618
Regulatory assets, long-term		640
Current portion of long-term regulatory assets
Regulatory Assets:
Regulatory assets, current	7,702	8,134
Pension and other postretirement benefits
Regulatory Assets:
Regulatory assets, long-term	105,546	111,121
Income taxes
Regulatory Assets:
Regulatory assets, long-term	47,567	47,177
Deferred construction accounting costs
Regulatory Assets:
Regulatory assets, long-term	15,251	15,521
Unamortized loss on reacquired debt
Regulatory Assets:
Regulatory assets, long-term	10,068	10,405
System reliability - vegetation management
Regulatory Assets:
Regulatory assets, long-term	2,871	5,337
Storm costs
Regulatory Assets:
Regulatory assets, long-term	3,836	4,183
Asset retirement obligation.
Regulatory Assets:
Regulatory assets, long-term	5,881	5,145
Customer programs
Regulatory Assets:
Regulatory assets, long-term	5,450	5,253
Missouri solar initiative
Regulatory Assets:
Regulatory assets, long-term	$ 1,140
Number of solar rebate applications processed | item	70
Rebate Commitments	$ 1,100
Unamortized loss on interest rate derivative
Regulatory Assets:
Regulatory assets, long-term	920	943
Deferred operating and maintenance expense
Regulatory Assets:
Regulatory assets, long-term	745	910
Other
Regulatory Assets:
Regulatory assets, long-term	1,578	2,179
Ice storm and tornado cost
Regulatory Assets:
Regulatory assets, long-term	3,100
Electric | Unsettled derivative losses- electric segment
Regulatory Assets:
Regulatory assets, long-term	$ 8,983	$ 9,037