Business Segment Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Sales and other operating revenue:	$ 310.5	$ 323.9
Adjusted EBITDA	53.0	47.9
Depreciation and amortization expense:	28.2	23.8
Capital expenditures:	13.8	8.3
Segment Assets [Abstract]
Tax assets	12.2	11.6
Assets held for sale	0.8	12.3
Total assets	2,189.8	2,255.5	$ 2,255.5
Coal	64.5		76.5
Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	2,176.8	2,231.6
Service Life | Indiana Harbor
Segment Reporting Information [Line Items]
Depreciation	$ 2.3	$ 1.1
Depreciation per share (in USD per share)	$ 0.04	$ 0.02
Domestic Coke
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 54.3	$ 52.7
Depreciation and amortization expense:	20.3	18.2
Capital expenditures:	10.0	8.0
Domestic Coke | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	1,502.7	1,534.2
Brazil Coke
Segment Reporting Information [Line Items]
Adjusted EBITDA	2.3	4.1
Depreciation and amortization expense:	0.2	0.2
Brazil Coke | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	59.8	58.8
Coal Logistics
Segment Reporting Information [Line Items]
Adjusted EBITDA	15.1	2.6
Depreciation and amortization expense:	5.4	1.8
Capital expenditures:	3.4	0.2
Coal Logistics | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	529.0	532.0
Coal Mining
Segment Reporting Information [Line Items]
Adjusted EBITDA	(4.1)	(3.1)
Depreciation and amortization expense:	1.5	2.8
Coal Mining | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	6.5	8.2
Coal	5.0		$ 3.3
Coal Mining | Service Life
Segment Reporting Information [Line Items]
Depreciation	$ 0.5	$ 2.0
Depreciation per share (in USD per share)	$ 0.01	$ 0.03
Corporate and Other, including legacy costs
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ (14.6)	$ (8.4)
Depreciation and amortization expense:	0.8	0.8
Capital expenditures:	0.4	0.1
Corporate and Other, including legacy costs | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	78.8	98.4
Operating Segments | Domestic Coke
Segment Reporting Information [Line Items]
Sales and other operating revenue:	289.0	303.1
Operating Segments | Brazil Coke
Segment Reporting Information [Line Items]
Sales and other operating revenue:	7.7	9.9
Operating Segments | Coal Logistics
Segment Reporting Information [Line Items]
Sales and other operating revenue:	13.0	7.3
Operating Segments | Coal Logistics intersegment sales
Segment Reporting Information [Line Items]
Sales and other operating revenue:	5.2	4.7
Operating Segments | Coal Mining
Segment Reporting Information [Line Items]
Sales and other operating revenue:	0.8	3.6
Operating Segments | Coal Mining intersegment sales
Segment Reporting Information [Line Items]
Sales and other operating revenue:	21.3	24.2
Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales and other operating revenue:	$ (26.5)	$ (28.9)