Impact of adoption of New Revenue Standard on Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Systems and components revenues	$ 19,466	$ 26,726	$ 63,538	$ 88,077
Gross profit	7,486	11,298	22,122	35,816
Income (loss) from operations	(1,093)	1,268	(6,149)	4,699
Income (loss) before income taxes	(907)	1,296	(5,685)	4,964
Net loss	(1,099)	1,230	(6,402)	4,159
Systems and components
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Systems and components revenues	17,140	$ 24,537	55,947	$ 82,822
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Systems and components revenues	19,359		63,202
Gross profit	7,379		21,786
Income (loss) from operations	(1,200)		(6,485)
Income (loss) before income taxes	(1,014)		(6,021)
Net loss	(1,206)		(6,738)
Calculated under Revenue Guidance in Effect before Topic 606 | Systems and components
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Systems and components revenues	17,033		55,611
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	107		336
Gross profit	107		336
Income (loss) from operations	107		336
Income (loss) before income taxes	107		336
Net loss	107		336
Accounting Standards Update 2014-09 | Difference Between Revenue Guidance in Effect Before and After Topic 606 | Systems and components
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Systems and components revenues	$ 107		$ 336