Revenue -Disaggregation of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2021	Jun. 27, 2020	Jul. 03, 2021	Jun. 27, 2020
Disaggregation of Revenue [Line Items]
Total net revenues	$ 13,813	$ 28,842	$ 30,054	$ 47,682
TFE
Disaggregation of Revenue [Line Items]
Total net revenues	5,369	16,595	14,607	24,557
TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	4,005	15,287	11,550	21,856
TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	1,364	1,308	3,057	2,701
Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	8,444	12,247	15,447	23,125
HDD | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	5,319	16,532	10,540	24,286
HDD | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	3,955	15,226	7,539	21,587
HDD | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	1,364	1,306	3,001	2,699
DCP | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	3		17
DCP | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	3		3
DCP | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	0		14
PV | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	47	63	200	271
PV | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	47	61	158	269
PV | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	0	2	42	2
ASP | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	0		3,850
ASP | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	0		3,850
ASP | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	0		0
Military Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	4,958	5,446	8,209	10,811
Commercial Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	50	39	178	118
Repair and Other Services | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	274	645	716	1,075
Product | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	5,282	6,130	9,103	12,004
Firm Fixed Price [Member] | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	1,543	5,462	3,348	9,892
Cost Plus Fixed Fee [Member] | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	1,619	655	2,996	1,229
Times and Materials | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	0	0	0	0
Technology Development | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	$ 3,162	$ 6,117	$ 6,344	$ 11,121