Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2012
Site Contingency [Line Items]
Proceeds from Legal Settlements		$ 110,000
Recovery of Direct Costs	$ 37,000
Huntsville Site [Member]
Site Contingency [Line Items]
Environmental Remediation Expense To Date	6,000
Additional Expected Project Expenditures Low Estimate	4,500
Additional Expected Project Expenditures High Estimate	10,000
Groundwater Removal [Member] | Norco Site [Member]
Site Contingency [Line Items]
Environmental Remediation Expense To Date	56,000
Additional Expected Project Expenditures Low Estimate	18,500
Additional Expected Project Expenditures High Estimate	29,000
Investigation Report [Member] | Huntsville Site [Member]
Site Contingency [Line Items]
Additional Expected Project Expenditures Low Estimate	200
Additional Expected Project Expenditures High Estimate	$ 400