Revenue -Disaggregation of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total net revenues	$ 24,827	$ 17,974
TFE
Disaggregation of Revenue [Line Items]
Total net revenues	18,945	12,789
TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	17,423	10,396
TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	1,522	2,393
Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	5,882	5,185
HDD | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	12,572	12,748
HDD | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	11,050	10,393
HDD | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	1,522	2,355
DCP | TFE
Disaggregation of Revenue [Line Items]
Total net revenues		1
DCP | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues		1
PV | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	6,373	40
PV | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	6,373	2
PV | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues		38
Military Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	1,813	2,254
Commercial Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	318
Repair and Other Services | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	561	429
Product | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	2,692	2,683
FFP | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	1,692	692
CPFF | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	1,496	1,790
Times and Materials | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	2	20
Technology Development | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	$ 3,190	$ 2,502