Revenue, Gross Profit, Gross Profit Margin and Operating Income (Loss) by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 02, 2020	Sep. 27, 2019	Oct. 02, 2020	Sep. 27, 2019
Segment Reporting Information [Line Items]
Revenue	$ 142,929	$ 154,066	$ 443,125	$ 466,397
Gross Profit	$ 59,105	$ 64,054	$ 182,252	$ 196,125
Gross profit margin percentage	41.40%	41.60%	41.10%	42.10%
Operating Income (Loss)	$ 11,866	$ 12,801	$ 38,817	$ 42,299
Operating Segments | Photonics
Segment Reporting Information [Line Items]
Revenue	46,394	54,570	149,337	172,081
Gross Profit	$ 20,166	$ 25,289	$ 65,725	$ 79,911
Gross profit margin percentage	43.50%	46.30%	44.00%	46.40%
Operating Income (Loss)	$ 7,026	$ 10,661	$ 22,878	$ 34,637
Operating Segments | Vision
Segment Reporting Information [Line Items]
Revenue	64,299	69,923	198,047	201,754
Gross Profit	$ 24,586	$ 26,922	$ 75,676	$ 78,106
Gross profit margin percentage	38.20%	38.50%	38.20%	38.70%
Operating Income (Loss)	$ 3,799	$ 5,830	$ 14,098	$ 14,602
Operating Segments | Precision Motion
Segment Reporting Information [Line Items]
Revenue	32,236	29,573	95,741	92,562
Gross Profit	$ 15,011	$ 12,504	$ 42,753	$ 39,784
Gross profit margin percentage	46.60%	42.30%	44.70%	43.00%
Operating Income (Loss)	$ 7,675	$ 5,221	$ 20,728	$ 16,839
Unallocated Corporate and Shared Services
Segment Reporting Information [Line Items]
Gross Profit	(658)	(661)	(1,902)	(1,676)
Operating Income (Loss)	$ (6,634)	$ (8,911)	$ (18,887)	$ (23,779)