Goodwill By Reportable Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 362,217	$ 259,357
Accumulated impairment of goodwill	(151,229)	(151,229)
Total	210,988	108,128	$ 103,456
Photonics
Goodwill [Line Items]
Goodwill	170,818	136,278
Accumulated impairment of goodwill	(102,461)	(102,461)
Total	68,357	33,817
Vision
Goodwill [Line Items]
Goodwill	157,436	89,116
Accumulated impairment of goodwill	(31,722)	(31,722)
Total	125,714	57,394
Precision Motion
Goodwill [Line Items]
Goodwill	33,963	33,963
Accumulated impairment of goodwill	(17,046)	(17,046)
Total	$ 16,917	$ 16,917