Contingencies (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Site Contingency [Line Items]
Accrual for environmental loss contingencies	$ 8,700,000	$ 9,100,000
Picton, Ontario Facility
Site Contingency [Line Items]
Increase due to charge to establish a liability for environmental investigation and remediation activities		$ 1,500,000	$ 3,300,000
Minimum
Site Contingency [Line Items]
Possible royalty repayment	0
Maximum
Site Contingency [Line Items]
Possible royalty repayment	4,700,000
NACoal
Site Contingency [Line Items]
Legal matter resolution charge	$ 3,300,000