Restructuring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring expense	$ 5,599	$ 644	$ 2,586
Performance Alloys and Composites
Restructuring Cost and Reserve [Line Items]
Restructuring expense	0	(16)	2,586
Advanced Materials
Restructuring Cost and Reserve [Line Items]
Restructuring expense	5,599	0	0
Precision Coatings
Restructuring Cost and Reserve [Line Items]
Restructuring expense	0	431	0
Other
Restructuring Cost and Reserve [Line Items]
Restructuring expense	$ 0	$ 229	$ 0