Regulatory Matters (Details 2) (USD $) In Thousands, unless otherwise specified			6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Current Recovery Period	Jun. 30, 2013 Cost of removal	Dec. 31, 2012 Cost of removal	Jun. 30, 2013 Income taxes	Dec. 31, 2012 Income taxes	Jun. 30, 2013 Deferred construction accounting costs - fuel	Dec. 31, 2012 Deferred construction accounting costs - fuel	Jun. 30, 2013 Unamortized gain on interest rate derivative	Dec. 31, 2012 Unamortized gain on interest rate derivative	Jun. 30, 2013 Pension and other postretirement benefits	Dec. 31, 2012 Pension and other postretirement benefits	Jun. 30, 2013 Over recovered fuel costs	Dec. 31, 2012 Over recovered fuel costs	Jun. 30, 2013 Current portion of long-term regulatory liabilities	Dec. 31, 2012 Current portion of long-term regulatory liabilities	Jun. 30, 2013 SWPA payment for Ozark Beach lost generation	Dec. 31, 2012 SWPA payment for Ozark Beach lost generation	Jun. 30, 2013 Pension and other postretirement benefits	Dec. 31, 2012 Pension and other postretirement benefits	Jun. 30, 2013 Income taxes	Dec. 31, 2012 Income taxes	Jun. 30, 2013 Deferred construction accounting costs.	Dec. 31, 2012 Deferred construction accounting costs.	Jun. 30, 2013 Unamortized loss on reacquired debt	Dec. 31, 2012 Unamortized loss on reacquired debt	Jun. 30, 2013 System reliability - vegetation management	Dec. 31, 2012 System reliability - vegetation management	Jun. 30, 2013 Storm costs	Dec. 31, 2012 Storm costs	Jun. 30, 2013 Asset retirement obligation	Dec. 31, 2012 Asset retirement obligation	Jun. 30, 2013 Customer programs	Dec. 31, 2012 Customer programs	Jun. 30, 2013 Unamortized loss on interest rate derivative	Dec. 31, 2012 Unamortized loss on interest rate derivative	Jun. 30, 2013 Other	Dec. 31, 2012 Other	Jun. 30, 2013 Deferred operating and maintenance expenses	Dec. 31, 2012 Deferred operating and maintenance expenses	Jun. 30, 2013 Under recovered fuel costs	Dec. 31, 2012 Under recovered fuel costs	Jun. 30, 2013 Current portion of long-term regulatory assets	Dec. 31, 2012 Current portion of long-term regulatory assets	Jun. 30, 2013 Electric Unsettled derivative losses	Dec. 31, 2012 Electric Unsettled derivative losses
Regulatory Assets:
Regulatory assets, current	$ 6,478	$ 6,377																																								$ 401	$ 2,885	$ 6,077	$ 3,492
Regulatory assets, long-term	234,496	243,958																		130,626	136,480	47,816	48,759	16,496	16,717	11,415	12,142	8,235	9,002	5,257	4,828	4,554	4,430	4,702	4,356	1,013	1,147	980	669	2,288	2,049	819	314	(6,077)	(3,492)	6,372	6,557
Regulatory assets, total	240,974	250,335
Period to recover costs in Missouri, Kansas and Oklahoma rates			12 months
Regulatory Liabilities:
Regulatory liabilities, current	5,003	5,470												1,652	2,381	3,351	3,089
Regulatory liabilities, long-term	133,895	131,888		90,278	83,368	11,863	11,972	8,083	8,156	3,456	3,541	1,323	2,007	1,409	3,691	(3,351)	(3,089)	20,834	22,242
Regulatory liabilities, total	$ 138,898	$ 137,358