Business Segment Information Business Segment Information - Legacy Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Defined benefit plan expense			$ (13.1)	$ (0.2)
Operating income (loss)	$ 23.1	$ 25.9	55.0	(40.8)
Other Segments
Segment Reporting Information [Line Items]
Royalty income	0.3	0.3	0.4	0.6
Black lung charges	(1.4)	(0.5)	(3.3)	(1.5)
Postretirement benefit plan (expense) benefit	(0.1)	0.2	3.7	0.8
Defined benefit plan expense	0.0	(0.1)	(13.1)	(0.2)
Workers compensation expense	(0.2)	(1.0)	(1.6)	(3.3)
Operating income (loss)	$ (1.4)	$ (1.1)	$ (13.9)	$ (3.6)