Restructuring (Details) $ in Thousands	3 Months Ended
	Mar. 27, 2020 USD ($) Employee	Mar. 29, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2,164	$ 0
Performance Alloys and Composites
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,200
Severance Costs	500
Remaining severance payments	$ 500
Number of positions eliminated | Employee	63
Other Restructuring Costs	$ 1,300
Restructuring cost, expected	$ 6,000