Discontinued Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property, Plant and Equipment, Additions	$ 3.9	$ 8.9	$ 51.0
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	0.0	6.1	20.1
Proceeds from disposal and sale of business interests	0.0	1.6	0.0
Revenues	1.4	24.2	70.9
Cost of revenues	(2.4)	(24.8)	(19.8)
Income / (loss) from discontinued operations before income tax	(1.0)	(0.6)	47.6
Income tax expense / (benefit) from discontinued operations	(0.2)	0.1	14.1
Net income / (loss) from discontinued operations	(0.8)	5.4	53.6
Cash Provided by (Used in) Operating Activities, Discontinued Operations	(0.8)	3.2	21.3
Cash Provided by (Used in) Investing Activities, Discontinued Operations	(1.6)	4.9	(51.0)
Settlement of Joint Operating Agreement			19.4
Disposal Group, Including Discontinued Operation, Fixed-Asset Impairment	0.0	0.0	(3.5)
Disposal Group, Including Discontinued Operation, Asset Retirement Obligation, Revision of Estimate			22.5
Stuart and Killen [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property, Plant and Equipment, Additions			51.0
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax			$ 20.0
Conesville [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property, Plant and Equipment, Additions	3.4
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax		$ 4.5
Forecast [Member] | Conesville [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property, Plant and Equipment, Additions	$ 4.0