Information for Each Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Segment Reporting Information [Line Items]
Total segment net revenues	$ 26,098	$ 30,963	$ 44,072	$ 61,351
Income (loss) from operations	65	1,339	(5,056)	3,430
Interest income and other income (expense), net	133	127	278	237
Income (loss) before income taxes	198	1,466	(4,778)	3,667
TFE
Segment Reporting Information [Line Items]
Total segment net revenues	20,848	22,426	33,637	43,910
Photonics
Segment Reporting Information [Line Items]
Total segment net revenues	5,250	8,537	10,435	17,441
Operating Segments
Segment Reporting Information [Line Items]
Income (loss) from operations	776	2,513	(2,943)	5,836
Operating Segments | TFE
Segment Reporting Information [Line Items]
Income (loss) from operations	1,220	1,749	(1,289)	3,608
Operating Segments | Photonics
Segment Reporting Information [Line Items]
Income (loss) from operations	(444)	764	(1,654)	2,228
Unallocated Amount to Segment
Segment Reporting Information [Line Items]
Unallocated costs	$ (711)	$ (1,174)	$ (2,113)	$ (2,406)