Income Tax Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Current Tax Expense (Benefit) [Abstract]
Federal	$ 0	[1]	$ 0	[1]
State	0.1	[1]	0	[1]
Total Current Tax Expense	0.1		0
Deferred Tax Expense (Benefit) [Abstract]
Federal	4.8		6.3
State	1.5		2.7
Investment Tax Credit Amortization	(0.2)		(0.2)
Total Deferred Tax Expense	6.1		8.8
Total Income Tax Expense	6.2		8.8
Effective Income Tax Rate	13.40%		20.70%
Federal Statutory Income Tax Rate	41.00%
Uncertain Tax Positions [Abstract]
Gross Unrecognized Tax Benefits	2.0				2.0
Unrecognized Tax Benefits that Would Favorably Impact Effective Tax Rate	$ 0.3

[1] For the three months ended March 31, 2015 and 2014, the federal and state current tax expense was minimal due to the utilization of NOL carryforwards from prior periods. The NOL carryforwards resulted from the bonus depreciation provisions of the Tax Increase Prevention Act of 2014 and the American Taxpayer Relief Act of 2012.