Goodwill and Other Intangible Assets - Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2016
Goodwill [Roll Forward]
Goodwill, beginning of period		$ 71.1	$ 71.1
Goodwill adjustments			5.8
Goodwill, end of period	$ 76.9		76.9
Domestic Coke
Goodwill [Roll Forward]
Goodwill, beginning of period		3.4	3.4
Goodwill adjustments			0.0
Goodwill, end of period	3.4		3.4
Coal Logistics
Goodwill [Roll Forward]
Goodwill, beginning of period		67.7	67.7
Goodwill adjustments	6.4	$ (0.6)	5.8
Goodwill, end of period	$ 73.5		$ 73.5