Purchased Intangible Assets - Details of Finite-lived Intangible Assets by Segment (Detail) - USD ($) $ in Thousands	Jun. 27, 2020	Dec. 28, 2019
Finite-Lived Intangible Assets [Line Items]
Finite Lived, Gross Carrying Amount	$ 8,387
Accumulated Amortization	(8,373)	$ (8,113)
Finite Lived, Net Carrying Amount	14	$ 274
TFE
Finite-Lived Intangible Assets [Line Items]
Finite Lived, Gross Carrying Amount	7,172
Accumulated Amortization	(7,172)
Finite Lived, Net Carrying Amount	0
Photonics
Finite-Lived Intangible Assets [Line Items]
Finite Lived, Gross Carrying Amount	1,215
Accumulated Amortization	(1,201)
Finite Lived, Net Carrying Amount	$ 14