Contingencies (Narrative) (Details) - USD ($)	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Loss Contingencies [Line Items]
Accrual for environmental investigation and remediation activities	$ 9,200,000	$ 9,100,000	$ 9,300,000
Minimum
Loss Contingencies [Line Items]
Estimate of possible loss	0
Maximum
Loss Contingencies [Line Items]
Estimate of possible loss	$ 5,400,000
Ohio Dormant Mineral Act, Mineral Abandonment Case
Loss Contingencies [Line Items]
Mineral interest abandonment statutory period	20 years
Estimate of possible loss	$ 4,500,000