Summary of Restructuring Costs for Each Segment and Unallocated Corporate Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	$ 346	$ 2,970	$ 5,840
2016 Restructuring
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	332	3,049	3,148
Cumulative Costs	6,529
2016 Restructuring | Photonics
Restructuring Cost And Reserve [Line Items]
Restructuring Costs		813	55
Cumulative Costs	868
2016 Restructuring | Vision
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	331	1,862	2,200
Cumulative Costs	4,393
2016 Restructuring | Precision Motion
Restructuring Cost And Reserve [Line Items]
Restructuring Costs		106	833
Cumulative Costs	939
2016 Restructuring | Unallocated Corporate and Shared Services
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	1	268	60
Cumulative Costs	329
2015 Restructuring
Restructuring Cost And Reserve [Line Items]
Restructuring Costs			1,484
2015 Restructuring | Photonics
Restructuring Cost And Reserve [Line Items]
Restructuring Costs			542
2015 Restructuring | Vision
Restructuring Cost And Reserve [Line Items]
Restructuring Costs			525
2015 Restructuring | Precision Motion
Restructuring Cost And Reserve [Line Items]
Restructuring Costs			79
2015 Restructuring | Unallocated Corporate and Shared Services
Restructuring Cost And Reserve [Line Items]
Restructuring Costs			338
2011 Restructuring
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	14	(79)	1,208
Cumulative Costs	5,197
2011 Restructuring | Photonics
Restructuring Cost And Reserve [Line Items]
Restructuring Costs		(188)
Cumulative Costs	1,751
2011 Restructuring | Vision
Restructuring Cost And Reserve [Line Items]
Cumulative Costs	48
2011 Restructuring | Precision Motion
Restructuring Cost And Reserve [Line Items]
Cumulative Costs	122
2011 Restructuring | Unallocated Corporate and Shared Services
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	14	$ 109	$ 1,208
Cumulative Costs	$ 3,276