Commitments And Contingencies (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) Foreign_Countries States Site	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Number of Superfund sites with operations and maintenance | Site	2
Number of states in which company performs environmental remediation | States	4
Number of foreign countries with environmental remediations | Foreign_Countries	1
Number of sites with environmental remediations | Site	7
Portion of environmental liabilities indemnified by Corus Group Ltd.	$ 10.1	$ 10.2
Asset retirement obligation	$ 6.2	6.1
Estimated time frame of disbursements	10 years
Other Long-Term Liabilities and Accrued Liabilities
Loss Contingencies [Line Items]
Reserves for environmental remediation liabilities	$ 21.9	$ 22.1