Information for Each Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Total segment net revenues	$ 19,466	$ 26,726	$ 63,538	$ 88,077
Income (loss) from operations	(1,093)	1,268	(6,149)	4,699
Interest income and other income (expense), net	186	28	464	265
Income (loss) before income taxes	(907)	1,296	(5,685)	4,964
TFE
Segment Reporting Information [Line Items]
Total segment net revenues	12,108	17,177	45,745	61,087
Photonics
Segment Reporting Information [Line Items]
Total segment net revenues	7,358	9,549	17,793	26,990
Operating Segments
Segment Reporting Information [Line Items]
Income (loss) from operations	(219)	2,630	(3,163)	8,467
Operating Segments | TFE
Segment Reporting Information [Line Items]
Income (loss) from operations	(907)	1,213	(2,197)	4,821
Operating Segments | Photonics
Segment Reporting Information [Line Items]
Income (loss) from operations	688	1,417	(966)	3,646
Unallocated Amount to Segment
Segment Reporting Information [Line Items]
Unallocated costs	$ (874)	$ (1,362)	$ (2,986)	$ (3,768)