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Summary of Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
USD ($)
Customer
Segment
Dec. 31, 2016
USD ($)
Customer
Summary Of Significant Accounting Policies [Line Items]    
Deferred revenue-current $ 445,000 $ 149,000
Number of major customers representing outstanding trade receivables | Customer 3 3
Protracted length of inventory 1 year  
Inventory valuation reserves $ 100,000 $ 100,000
Estimated useful life of intangible assets 10 years  
Number of reportable segments | Segment 1  
Period of warranty 1 year  
Warranty claim liability $ 0 $ 0
Trade Accounts Receivable | Customer Concentration Risk    
Summary Of Significant Accounting Policies [Line Items]    
Concentration risk, percentage 53.00% 46.00%
Maximum    
Summary Of Significant Accounting Policies [Line Items]    
Long-term deferred revenue $ 100,000 $ 100,000
Shelf lives of inventory 24 months  
Estimated useful life of property and equipment 5 years  
Minimum    
Summary Of Significant Accounting Policies [Line Items]    
Shelf lives of inventory 18 months  
Estimated useful life of property and equipment 3 years