Property, Plant, and Equipment (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Missouri	Dec. 31, 2011 Missouri	Dec. 31, 2011 Tennessee	Dec. 31, 2010 Tennessee	Dec. 31, 2013 Non-Leasing Group
Future minimum rent expense on non-Leasing Group leases
2014								$ 5.3
2015								3.5
2016								2.6
2017								1.6
2018								0.7
Thereafter								1.0
Payments from insurance carriers					35.0		27.5
Insurance recoveries pertaining to replacement of or repairs to damaged property, plant, and equipment					22.7		12.6
Net book value of damaged property, plant, and equipment					5.7		2.3
Gains on disposition of flood-damaged property, plant and equipment	0	0.4	17.6	0.4	17.0	0.6	9.7
Net book value of non-operating plants	$ 24.3