Impact of adoption of New Revenue Standard on Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Systems and components revenues	$ 23,335	$ 29,863	$ 38,807	$ 58,286
Total net revenues	26,098	30,963	44,072	61,351
Gross profit	9,761	11,470	14,636	24,517
Income (loss) from operations	65	1,339	(5,056)	3,430
Income (loss) before income taxes	198	1,466	(4,778)	3,667
Net loss	(167)	$ 1,100	(5,303)	$ 2,929
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Systems and components revenues	23,235		38,578
Total net revenues	25,998		43,843
Gross profit	9,661		14,407
Income (loss) from operations	(35)		(5,285)
Income (loss) before income taxes	98		(5,007)
Net loss	(267)		(5,532)
Accounting Standards Update 2014-09 | Difference Between Revenue Guidance in Effect Before and After Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Systems and components revenues	100		229
Total net revenues	100		229
Gross profit	100		229
Income (loss) from operations	100		229
Income (loss) before income taxes	100		229
Net loss	$ 100		$ 229