Goodwill By Reportable Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill	$ 368,891	$ 362,217
Accumulated impairment of goodwill	(151,229)	(151,229)
Total	217,662	210,988
Photonics
Goodwill [Line Items]
Goodwill	168,955	170,818
Accumulated impairment of goodwill	(102,461)	(102,461)
Total	66,494	68,357
Vision
Goodwill [Line Items]
Goodwill	155,017	157,436
Accumulated impairment of goodwill	(31,722)	(31,722)
Total	123,295	125,714
Precision Motion
Goodwill [Line Items]
Goodwill	44,919	33,963
Accumulated impairment of goodwill	(17,046)	(17,046)
Total	$ 27,873	$ 16,917

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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-Publisher FASB
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Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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