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Summary of Significant Accounting Policies - Additional Information (Detail)
shares in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2015
USD ($)
Customer
Sep. 30, 2014
USD ($)
Sep. 30, 2015
USD ($)
Customer
Segment
Sep. 30, 2014
USD ($)
Dec. 31, 2014
USD ($)
Customer
Nov. 30, 2010
shares
Aug. 31, 2009
shares
Summary Of Significant Accounting Policies [Line Items]              
Reserves for uncollectible accounts $ 0   $ 0   $ 0    
Number of major customers representing outstanding trade receivables | Customer 2   2   1    
Life of inventory     2 years        
Protracted length of inventory     1 year        
Inventory valuation reserves $ 1,300,000   $ 1,300,000   $ 100,000    
Capitalized costs for enhancement of enterprise resource planning software system and other internal use software 0 $ 1,800,000 $ 0 $ 1,800,000      
Estimated useful life of intangible assets     10 years        
Number of reportable segments | Segment     1        
Impairment charges on long-lived assets 0 0 $ 0 0      
Tax year subject to examination     The Company's US federal and California tax years through 2014 remain subject to examination by the taxing jurisdictions due to unutilized net operating losses and research credits.        
Period of warranty     1 year        
Warranty claim liability $ 0   $ 0   $ 0    
Computer Software, Intangible Asset              
Summary Of Significant Accounting Policies [Line Items]              
Enterprise resource planning system, estimated useful life     5 years        
2009 Unit Offering              
Summary Of Significant Accounting Policies [Line Items]              
Warrants to purchase an aggregate shares of common stock | shares             2.4
2010 Unit Offering              
Summary Of Significant Accounting Policies [Line Items]              
Warrants to purchase an aggregate shares of common stock | shares           3.7  
Other income, net              
Summary Of Significant Accounting Policies [Line Items]              
Reclassified amortization of premium from purchase of fixed income securities   $ 100,000   $ 300,000      
Trade Accounts Receivable | Customer Concentration Risk              
Summary Of Significant Accounting Policies [Line Items]              
Concentration risk, percentage     42.00%   36.00%    
Minimum              
Summary Of Significant Accounting Policies [Line Items]              
Estimated useful life of property and equipment     3 years        
Maximum              
Summary Of Significant Accounting Policies [Line Items]              
Estimated useful life of property and equipment     5 years