Business Segment Information - Segment Profit or Loss (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Sales and other operating revenues	$ 368.9	$ 364.5	$ 367.0	$ 350.5	$ 359.6	$ 339.0	$ 323.2	$ 309.7	$ 1,450.9	$ 1,331.5	$ 1,223.3
Adjusted EBITDA									263.2	234.7	217.0
Depreciation and amortization expense									141.6	128.2	114.2
Capital expenditures									100.3	75.6	63.7
Domestic Coke | Service Life
Segment Reporting Information [Line Items]
Depreciation and amortization expense									$ 9.2
Additional depreciation per common share (USD per share)									$ 0.14
Corporate and Other
Segment Reporting Information [Line Items]
Sales and other operating revenues									$ 0.0	0.0	1.5
Adjusted EBITDA									(35.7)	(43.2)	(57.0)
Depreciation and amortization expense									1.4	0.5	4.7
Capital expenditures									0.0	2.4	1.7
Coal Mining
Segment Reporting Information [Line Items]
Adjusted EBITDA									(9.8)	(10.5)	(15.0)
Operating Segments | Domestic Coke
Segment Reporting Information [Line Items]
Sales and other operating revenues									1,308.3	1,195.0	1,097.6
Adjusted EBITDA									207.9	188.9	193.9
Depreciation and amortization expense									114.4	102.6	84.0
Capital expenditures									95.1	68.8	44.6
Operating Segments | Brazil Coke
Segment Reporting Information [Line Items]
Sales and other operating revenues									40.4	43.4	39.5
Adjusted EBITDA									18.4	18.2	16.2
Depreciation and amortization expense									0.7	0.7	0.7
Operating Segments | Logistics
Segment Reporting Information [Line Items]
Sales and other operating revenues									102.2	93.1	84.7
Adjusted EBITDA									72.6	70.8	63.9
Depreciation and amortization expense									25.1	24.4	24.8
Capital expenditures									5.2	4.4	17.4
Elimination of intersegment sales
Segment Reporting Information [Line Items]
Sales and other operating revenues									(24.5)	(23.8)	(45.2)
Elimination of intersegment sales | Logistics
Segment Reporting Information [Line Items]
Sales and other operating revenues									24.5	23.8	23.2
Corporate and Other intersegment sales
Segment Reporting Information [Line Items]
Sales and other operating revenues									$ 0.0	$ 0.0	$ 22.0