Revenue -Disaggregation of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Disaggregation of Revenue [Line Items]
Total net revenues	$ 28,842	$ 22,314	$ 47,682	$ 47,141
TFE
Disaggregation of Revenue [Line Items]
Total net revenues	16,595	13,264	24,557	32,209
TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	15,287	12,441	21,856	29,864
TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	1,308	823	2,701	2,345
Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	12,247	9,050	23,125	14,932
HDD | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	16,532	13,244	24,286	25,816
HDD | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	15,226	12,423	21,587	23,473
HDD | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	1,306	821	2,699	2,343
DCP | TFE
Disaggregation of Revenue [Line Items]
Total net revenues				2
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		2		2
PV | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	63	18	271	6,391
PV | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	61	18	269	6,391
PV | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues			2
Military Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	5,446	2,981	10,811	4,794
Commercial Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	39	182	118	500
Repair and Other Services | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	645	810	1,075	1,371
Product | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	6,130	3,973	12,004	6,665
Firm Fixed Price [Member] | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	5,462	3,085	9,892	4,777
Cost Plus Fixed Fee [Member] | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	655	1,992	1,229	3,488
Times and Materials | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues				2
Technology Development | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	$ 6,117	$ 5,077	$ 11,121	$ 8,267