Derivative Financial Instruments and Hedging (Details) € in Millions, lb in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) lb	Sep. 30, 2016 USD ($)	Sep. 30, 2017 EUR (€)
Derivative Instruments Gain Loss [Line Items]
Percentage of estimated annual nickel requirements			20.00%
Percentage Of Forecasted Natural Gas Usage Hedged for 2017			55.00%
Percentage Of Forecasted Natural Gas Usage Hedged for 2018			35.00%
Percentage of Forecasted Natural Gas Usage Hedged for 2019			30.00%
Reclassification of Cash Flow Hedge Gain (Loss) [Abstract]
Cash Flow Hedge Gain (Loss) To Be Reclassified Within Twelve Months			$ (1.7)
Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Other Comprehensive Income Effective Portion Net	$ 5.7	$ 3.0	(1.0)	$ 13.6
Cost Of Sales | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	0.8	(0.1)	2.2	(4.1)
Selling And Administrative Expenses | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Ineffective Portion And Amount Excluded From Effectiveness Testing Net	0.0	(0.3)	$ 0.0	(1.2)
Nickel
Derivative Instruments Gain Loss [Line Items]
Notional amount of nickel hedge (in pounds of nickel) | lb			17
Nickel and other raw material contracts | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Other Comprehensive Income Effective Portion Net	5.6	4.2	$ 1.2	13.0
Nickel and other raw material contracts | Cost Of Sales | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	(0.9)	(2.2)	(2.5)	(9.9)
Nickel and other raw material contracts | Selling And Administrative Expenses | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Ineffective Portion And Amount Excluded From Effectiveness Testing Net	0.0	0.0	0.0	0.0
Natural gas contracts | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Other Comprehensive Income Effective Portion Net	0.0	(1.2)	(2.1)	1.1
Natural gas contracts | Cost Of Sales | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	(0.7)	(1.3)	(2.8)	(7.2)
Natural gas contracts | Selling And Administrative Expenses | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Ineffective Portion And Amount Excluded From Effectiveness Testing Net	0.0	(0.3)	0.0	(1.2)
Foreign exchange contracts | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Other Comprehensive Income Effective Portion Net	0.1	0.0	(0.1)	(0.5)
Foreign exchange contracts | Cost Of Sales | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	2.4	3.4	7.5	13.0
Foreign exchange contracts | Selling And Administrative Expenses | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Ineffective Portion And Amount Excluded From Effectiveness Testing Net	0.0	0.0	0.0	0.0
Designated as Hedging Instrument | Foreign exchange forward | Cost Of Sales | Fair Value Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Net	(0.5)	(0.5)	(2.7)	(3.0)
Designated as Hedging Instrument | Foreign exchange forward | Maturity Dates Through 2017 [Member] | Fair Value Hedging
Derivative Instruments Gain Loss [Line Items]
Notional amount of derivative | €					€ 10.8
Designated as Hedging Instrument | Natural gas contracts | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Loss on Cash Flow Hedge Ineffectiveness		0.4		1.7
Not Designated as Hedging Instrument | Foreign exchange forward | Maturity Dates Through Q2 2018 [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount of derivative | €					€ 10.0
Not Designated as Hedging Instrument | Foreign exchange contracts | Cost Of Sales
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Net	$ (0.1)	$ (0.2)	$ (0.7)	$ (0.1)