Restructuring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring expense	$ 785	$ 5,599	$ 644
Performance Alloys and Composites
Restructuring Cost and Reserve [Line Items]
Restructuring expense	0	0	(16)
Advanced Materials
Restructuring Cost and Reserve [Line Items]
Restructuring expense	0	5,599	0
Precision Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring expense	328	0	431
Other
Restructuring Cost and Reserve [Line Items]
Restructuring expense	$ 457	$ 0	$ 229