Business Segment Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Sales and other operating revenue:	$ 292.6	$ 347.6	$ 603.1	$ 671.5
Adjusted EBITDA	46.5	33.4	90.3	81.3
Depreciation and amortization expense:	28.6	26.4	56.8	50.2
Capital expenditures:	16.4	14.2	30.2	22.5
Segment Assets [Abstract]
Tax assets	9.7	11.6	9.7	11.6
Assets held for sale	0.0	12.3	0.0	12.3
Total assets	2,142.0	2,255.5	2,142.0	2,255.5	$ 2,255.5
Coal	62.0		62.0		$ 76.5
Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	2,132.3	2,231.6	2,132.3	2,231.6
Service Life | Indiana Harbor
Segment Reporting Information [Line Items]
Depreciation	$ 1.3	$ 1.8	$ 3.6	$ 2.9
Depreciation per share (in USD per share)	$ 0.02	$ 0.03	$ 0.06	$ 0.04
Domestic Coke
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 51.0	$ 56.2	$ 105.3	$ 108.9
Depreciation and amortization expense:	19.7	20.0	40.0	38.2
Capital expenditures:	6.9	13.9	16.9	21.9
Domestic Coke | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	1,525.8	1,534.2	1,525.8	1,534.2
Brazil Coke
Segment Reporting Information [Line Items]
Adjusted EBITDA	2.4	2.6	4.7	6.7
Depreciation and amortization expense:	0.2	0.1	0.4	0.3
Brazil Coke | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	49.8	58.8	49.8	58.8
Coal Logistics
Segment Reporting Information [Line Items]
Adjusted EBITDA	5.4	5.0	11.3	7.6
Depreciation and amortization expense:	8.0	1.9	13.4	3.7
Capital expenditures:	9.0	0.3	12.4	0.5
Coal Logistics | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	518.6	532.0	518.6	532.0
Coal Logistics | Service Life
Segment Reporting Information [Line Items]
Depreciation			$ 2.2
Depreciation per share (in USD per share)			$ 0.03
Coal Mining
Segment Reporting Information [Line Items]
Adjusted EBITDA	(0.9)	(5.4)	$ (5.0)	(8.5)
Depreciation and amortization expense:	0.0	3.7	1.5	6.5
Coal Mining | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	0.0	8.2	0.0	8.2
Coal Mining | Service Life
Segment Reporting Information [Line Items]
Depreciation		$ 2.7		$ 4.7
Depreciation per share (in USD per share)		$ 0.04		$ 0.07
Corporate and Other, including legacy costs
Segment Reporting Information [Line Items]
Adjusted EBITDA	(11.4)	$ (25.0)	(26.0)	$ (33.4)
Depreciation and amortization expense:	0.7	0.7	1.5	1.5
Capital expenditures:	0.5	0.0	0.9	0.1
Corporate and Other, including legacy costs | Continuing Operations
Segment Assets [Abstract]
Assets excluding tax assets	38.1	98.4	38.1	98.4
Operating Segments | Domestic Coke
Segment Reporting Information [Line Items]
Sales and other operating revenue:	274.0	326.5	563.0	629.6
Operating Segments | Brazil Coke
Segment Reporting Information [Line Items]
Sales and other operating revenue:	7.4	8.5	15.1	18.4
Operating Segments | Coal Logistics
Segment Reporting Information [Line Items]
Sales and other operating revenue:	11.2	8.6	24.2	15.9
Operating Segments | Coal Logistics intersegment sales
Segment Reporting Information [Line Items]
Sales and other operating revenue:	5.2	4.9	10.4	9.6
Operating Segments | Coal Mining
Segment Reporting Information [Line Items]
Sales and other operating revenue:	0.0	4.0	0.8	7.6
Operating Segments | Coal Mining intersegment sales
Segment Reporting Information [Line Items]
Sales and other operating revenue:	0.7	24.8	22.0	49.0
Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales and other operating revenue:	$ (5.9)	$ (29.7)	$ (32.4)	$ (58.6)