Revenue - Disaggregation of Revenue from Contracts with Customers (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
TFE
Disaggregation of Revenue [Line Items]
Total net revenues	12,108	17,177	45,745	61,087
TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	9,527	15,895	39,145	57,284
TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	2,581	1,282	6,600	3,803
Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	7,358	9,549	17,793	26,990
HDD | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	12,057	16,902	45,651	38,678
HDD | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	9,476	15,620	39,090	34,875
HDD | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues	2,581	1,282	6,561	3,803
DCP | TFE
Disaggregation of Revenue [Line Items]
Total net revenues			1	13,138
DCP | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues			1	13,138
PV | TFE
Disaggregation of Revenue [Line Items]
Total net revenues	51	275	93	9,271
PV | TFE | Systems, Upgrades and Spare Parts
Disaggregation of Revenue [Line Items]
Total net revenues	51	275	54	9,271
PV | TFE | Field Service
Disaggregation of Revenue [Line Items]
Total net revenues			39
Military Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	4,202	6,989	8,601	20,908
Commercial Products | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	84	38	138	100
Repair and Other Services | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	746	333	1,463	727
Product | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	5,032	7,360	10,202	21,735
FFP | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	494	728	1,726	2,724
CPFF | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	1,819	1,446	5,829	2,516
Times and Materials | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	13	15	36	15
Technology Development | Photonics
Disaggregation of Revenue [Line Items]
Total net revenues	$ 2,326	$ 2,189	$ 7,591	$ 5,255