Revenue, Gross Profit and Operating Income (Loss) from Continuing Operations by Reportable Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 384,758	$ 373,598	$ 364,706
Gross Profit	162,452	157,890	150,167
Operating Income (Loss) from Continuing Operations	32,563	28,933	(16,806)
Photonics
Segment Reporting Information [Line Items]
Revenue	174,158	168,331	177,726
Gross Profit	76,696	73,602	74,224
Operating Income (Loss) from Continuing Operations	34,825	35,971	33,053
Vision
Segment Reporting Information [Line Items]
Revenue	122,250	124,725	122,187
Gross Profit	47,181	48,966	48,678
Operating Income (Loss) from Continuing Operations	(1,277)	(2,057)	(43,079)
Precision Motion
Segment Reporting Information [Line Items]
Revenue	88,350	80,542	64,793
Gross Profit	40,044	36,709	28,333
Operating Income (Loss) from Continuing Operations	21,101	16,877	13,023
Unallocated Corporate and Shared Services
Segment Reporting Information [Line Items]
Gross Profit	(1,469)	(1,387)	(1,068)
Operating Income (Loss) from Continuing Operations	$ (22,086)	$ (21,858)	$ (19,803)