Segment Reporting - Assets for Each Reportable Segment (Detail) - USD ($) $ in Thousands	Jun. 27, 2020	Dec. 28, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated total assets	$ 124,829	$ 126,322
Cash and investments	43,983	42,024
Restricted cash	787	787
Deferred income taxes	5,826	6,252
Other current assets	1,207	752
Common property, plant and equipment	1,414	1,307
Common operating lease right-of-use assets	1,815	1,898
Other assets	0	78
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated total assets	69,797	73,244
Operating Segments | TFE
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated total assets	43,175	51,153
Operating Segments | Photonics
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated total assets	$ 26,622	$ 22,071