Revenue -Disaggregation of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Disaggregation of Revenue [Line Items]
Total net revenues	$ 18,840	$ 24,827
TFE
Disaggregation of Revenue [Line Items]
Total net revenues	7,962	18,945
TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	6,569	17,423
TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	1,393	1,522
Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	10,878	5,882
HDD | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	7,754	12,572
HDD | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	6,361	11,050
HDD | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	1,393	1,522
DCP | TFE
Disaggregation of Revenue [Line Items]
Total net revenues
DCP | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues
DCP | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues
PV | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	208	6,373
PV | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	208	6,373
PV | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues
Military Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	5,365	1,813
Commercial Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	79	318
Repair and Other Services | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	430	561
Product | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	5,874	2,692
Firm Fixed Price [Member] | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	4,430	1,692
Cost Plus Fixed Fee [Member] | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	574	1,496
Times and Materials | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues		2
Technology Development | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	$ 5,004	$ 3,190