Depreciation and Amortization Expenses by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Depreciation and Amortization Expenses
Depreciation and amortization expenses	$ 9,040	$ 9,120	$ 18,114	$ 18,187
Unallocated Corporate and Shared Services
Depreciation and Amortization Expenses
Depreciation and amortization expenses	71	216	126	539
Photonics | Operating Segments
Depreciation and Amortization Expenses
Depreciation and amortization expenses	2,589	2,966	5,210	6,033
Vision | Operating Segments
Depreciation and Amortization Expenses
Depreciation and amortization expenses	5,197	5,097	10,226	10,271
Precision Motion | Operating Segments
Depreciation and Amortization Expenses
Depreciation and amortization expenses	$ 1,183	$ 841	$ 2,552	$ 1,344