Income Taxes (Deferred) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Asset retirement obligations and other	$ 0.9	$ 2.3
State net operating loss carryforward, non current	6.5	3.6
Federal net operating loss carryforward, non current	59.5	20.9
Total non current deferred tax assets	66.9	26.8
Property, plant, equipment, and intangible assets, non current	(609.5)	(557.6)
Other	0.0	(1.3)
Total non current deferred tax liabilities	(609.5)	(558.9)
Deferred tax liability, net	$ (542.6)	$ (532.1)