Depreciation and Amortization Expenses by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 28, 2018	Sep. 29, 2017
Depreciation and Amortization Expenses
Depreciation and amortization expenses	$ 9,199	$ 8,864	$ 27,386	$ 22,440
Photonics
Depreciation and Amortization Expenses
Depreciation and amortization expenses	2,997	3,666	9,030	10,693
Vision
Depreciation and Amortization Expenses
Depreciation and amortization expenses	5,100	4,362	15,371	9,276
Precision Motion
Depreciation and Amortization Expenses
Depreciation and amortization expenses	1,020	588	2,364	1,746
Unallocated Corporate and Shared Services
Depreciation and Amortization Expenses
Depreciation and amortization expenses	$ 82	$ 248	$ 621	$ 725