Revenue - Primary Geographical Markets (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total net revenues	$ 19,466	$ 26,726	$ 63,538	$ 88,077
Products Transferred at a Point in Time
Disaggregation of Revenue [Line Items]
Total net revenues	12,854		47,208
Products and Services Transferred Over Time
Disaggregation of Revenue [Line Items]
Total net revenues	6,612		16,330
United States
Disaggregation of Revenue [Line Items]
Total net revenues	7,155	10,294	20,177	29,879
Asia
Disaggregation of Revenue [Line Items]
Total net revenues	11,821	15,807	42,227	57,062
Europe
Disaggregation of Revenue [Line Items]
Total net revenues	457	94	937	605
Rest of World
Disaggregation of Revenue [Line Items]
Total net revenues	33	531	197	531
TFE
Disaggregation of Revenue [Line Items]
Total net revenues	12,108	17,177	45,745	61,087
TFE | Products Transferred at a Point in Time
Disaggregation of Revenue [Line Items]
Total net revenues	12,108		45,745
TFE | United States
Disaggregation of Revenue [Line Items]
Total net revenues	287	1,370	3,549	4,033
TFE | Asia
Disaggregation of Revenue [Line Items]
Total net revenues	11,821	15,807	42,196	57,054
Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	7,358	9,549	17,793	26,990
Photonics | Products Transferred at a Point in Time
Disaggregation of Revenue [Line Items]
Total net revenues	746		1,463
Photonics | Products and Services Transferred Over Time
Disaggregation of Revenue [Line Items]
Total net revenues	6,612		16,330
Photonics | United States
Disaggregation of Revenue [Line Items]
Total net revenues	6,868	8,924	16,628	25,846
Photonics | Asia
Disaggregation of Revenue [Line Items]
Total net revenues			31	8
Photonics | Europe
Disaggregation of Revenue [Line Items]
Total net revenues	457	94	937	605
Photonics | Rest of World
Disaggregation of Revenue [Line Items]
Total net revenues	$ 33	$ 531	$ 197	$ 531