Commitments and Contingencies, Environmental (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)
Environmental Contingency
Environmental accrual	$ 16.9	$ 16.9
Expected period related to remediation expenditures for environmental contingencies period		30 years
Potential increase in environmental costs	$ 12.2	$ 12.2
Time period within which Companys recorded estimate of its obligation may change	12 months
Minimum
Environmental Contingency
Period for final feasibility study		12 months
Maximum
Environmental Contingency
Period for final feasibility study		15 months