Restructuring (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 26, 2020 USD ($) Employee	Jun. 28, 2019 USD ($)	Jun. 26, 2020 USD ($) Employee	Jun. 28, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2,387	$ 0	$ 4,551	$ 0
Performance Alloys and Composites
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,400		4,600
Severance Costs	$ 900		$ 1,400
Number of positions eliminated | Employee	60		60
Other Restructuring Costs	$ 1,500		$ 3,100
Restructuring cost, expected	4,000		4,000
Performance Alloys and Composites | Other Liabilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring facility cost remaining	400		400
Performance Alloys and Composites | Accrued Liabilities [Member]
Restructuring Cost and Reserve [Line Items]
Remaining severance payments	$ 1,200		$ 1,200