Restructuring Costs (Details) - USD ($) $ in Thousands	12 Months Ended			40 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Restructuring Reserve [Roll Forward]
Restructuring costs (Note 5)	$ 8,359	$ 1,558	$ 7,353
Inventory Write-down			32,500
Depreciation	28,000	21,300	20,900
Gain (Loss) on Disposition of Business	(493)	3,739	(5,722)
Severance Costs			1,400
GA Reduction Effort [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	4,000	900
COVID19 [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	3,500
2017 Announced Restructuring Plan [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Beginning Balance	400
Payments for Restructuring	(700)
Restructuring Reserve, Ending Balance	0	400		$ 0
Actual Savings Achieved by Exit Plan	8,000
Restructuring costs (Note 5)	300	600	6,000	$ 9,600
Inventory Write-down		300	800
Depreciation		100
Share-based Payment Arrangement, Accelerated Cost			400
Bal Seal [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	500
U.K. Composites [Member]
Restructuring Reserve [Roll Forward]
Gain (Loss) on Disposition of Business	$ 500	$ (3,700)	(5,700)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax			1,700
Engineering Services [Member]
Restructuring Reserve [Roll Forward]
Gain (Loss) on Disposition of Assets			$ 700