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Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Jan. 01, 2017
Dec. 31, 2017
USD ($)
Customer
Dec. 31, 2016
USD ($)
Customer
Dec. 31, 2015
USD ($)
Revenue, Major Customer [Line Items]        
Gross deferred revenue   $ 4,659,000 $ 3,337,000  
Gross deferred cost of revenue   $ 2,135,000 $ 1,445,000  
Revenue recognized under multi-element   3.00% 3.00% 3.00%
Foreign currency gains (losses)   $ 323,000 $ (268,000) $ (161,000)
Maturity period of cash and cash equivalents     Less than three months  
Available-for-sale securities, failed auction, value   $ 3,000,000    
Number of customers accounted for trade account receivable | Customer   1 1  
Cost of advertising   $ 2,150,000 $ 1,818,000 $ 1,762,000
Product warranty period   2 years    
Percentage likelihood of tax benefit settlement   50.00%    
Recognition period of non performance based stock options   5 years    
Military Grade Products [Member]        
Revenue, Major Customer [Line Items]        
Extended warranty period 3 years      
Customer One [Member]        
Revenue, Major Customer [Line Items]        
Percentage of trade account receivable   17.50% 14.20%  
Maximum [Member]        
Revenue, Major Customer [Line Items]        
Recognition period   12 months    
Estimated useful life of intangible assets   20 years    
Minimum [Member]        
Revenue, Major Customer [Line Items]        
Recognition period   6 months    
Estimated useful life of intangible assets   3 years