Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	1 Months Ended		12 Months Ended	0 Months Ended			1 Months Ended
	Mar. 31, 2015	Aug. 31, 2014 property party	Sep. 30, 2013 property party	Dec. 31, 2012 property	May 30, 2012 action	Mar. 15, 2012 officer	Jan. 26, 2012 officer	Feb. 29, 2012 complaint
Commitments and contingencies
Comment letter period	30 days
Accruals for unrecognized tax benefits related to disposition	$ 33.0
Environmental Matters | Walter Coke, Inc.
Commitments and contingencies
Number of properties that the entity has agreed to remediate				23
Number of other PRP's in which "Offer to Conduct Work" letter was sent to		5	4
Number of residential properties whose sampling has been completed by EPA			1,100
Number of properties exceeding Regional Removal Management Levels (RML's)			400
Number of Phase I properties offered to Potentially Responsible Parties PRP's for cleanup			50
Number of Phase II Properties Offered to Other Potentially Responsible Parties for Clean Up		30
Securities Class Actions and Shareholder Derivative Actions
Commitments and contingencies
Number of executive directors as defendants						3	3
Number of actions					2
Number of complaints								3
Minimum
Commitments and contingencies
Number of years the Company remains subject to income tax in various states for prior periods	3 years
Number of years for which the tax years are typically subject to examination in the major non-U.S. jurisdictions	3 years
Maximum
Commitments and contingencies
Number of years the state impact of any federal changes remains subject to examination	5 years
Number of years the Company remains subject to income tax in various states for prior periods	11 years
Number of years for which the tax years are typically subject to examination in the major non-U.S. jurisdictions	6 years