Derivative Financial Instruments and Hedging (Details2) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	$ 8.1	$ 3.4
Derivative Fair Value Of Derivative Liability	3.3	10.4
Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	7.6	3.0
Derivative Fair Value Of Derivative Liability	3.3	10.4
Designated as Hedging Instrument | Nickel and other raw material contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	4.6	1.2
Designated as Hedging Instrument | Nickel and other raw material contracts | Other assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	2.4	0.8
Designated as Hedging Instrument | Nickel and other raw material contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	1.9	6.8
Designated as Hedging Instrument | Nickel and other raw material contracts | Other long-term liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.5	2.1
Designated as Hedging Instrument | Interest Rate Swap | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.3	0.2
Designated as Hedging Instrument | Interest Rate Swap | Other long-term liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.3	0.3
Designated as Hedging Instrument | Natural gas contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.3	0.8
Designated as Hedging Instrument | Natural gas contracts | Other assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.0	0.2
Designated as Hedging Instrument | Natural gas contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.1	0.1
Designated as Hedging Instrument | Natural gas contracts | Other long-term liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.2	0.3
Designated as Hedging Instrument | Foreign exchange contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.3	0.0
Designated as Hedging Instrument | Foreign exchange contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.0	0.6
Not Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.5	0.4
Not Designated as Hedging Instrument | Foreign exchange contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	$ 0.5	$ 0.4