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Stock-based Compensation (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Aug. 29, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of ownership interest       51.20%
Share-based Compensation [Abstract]        
Share-based compensation expense $ 1,630,000 $ 922,000 $ 1,815,000  
Stock Option Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Common stock, shares authorized (in shares) 5,200,000      
Maximum period for options grants in period 10 years      
Maximum period for options exercises in period 10 years      
Period for exercising vested option 12 months      
Shares Available for Grant [Roll Forward]        
Beginning of the period (in shares) 880,000 1,757,000    
Increase in pool (in shares) 1,200,000      
Options granted (in shares) (896,000) (962,000)    
Options exercised (in shares) 0 0    
Options forfeited, cancelled or expired (in shares) 200,000 85,000    
End of the period (in shares) 1,384,000 880,000 1,757,000  
Number of Options Outstanding [Roll Forward]        
Beginning of the period (in shares) 3,017,000 2,240,000    
Option granted (in shares) 896,000 962,000    
Options exercised (in shares) (323,000) (100,000)    
Options forfeited, cancelled or expired (in shares) (200,000) (85,000)    
End of the period (in shares) 3,390,000 3,017,000 2,240,000  
Exercisable (in shares) 1,835,000      
Weighted Average Exercise Price [Roll Forward]        
Beginning of the period (in dollars per share) $ 2.52 $ 2.03    
Option granted (in dollars per share) 5.17 3.58    
Options exercised (in dollars per share) 1.89 2.19    
Options forfeited, cancelled or expired (in dollars per share) 3.11 2.00    
End of the period (in dollars per share) 3.25 $ 2.52 $ 2.03  
Exercisable (in dollars per share) $ 2.48      
Total unrecognized compensation costs $ 1,600,000 $ 2,700,000    
Weighted average recognition period 2 years 6 months 2 years 4 months 24 days    
Share-based Compensation [Abstract]        
Share-based compensation expense $ 1,630,000 $ 922,000 $ 1,815,000  
Weighted-average assumptions [Abstract]        
Expected life 6 years 1 month 24 days 6 years 2 months 16 days 6 years 9 months 29 days  
Risk-free interest rates 2.03% 1.46% 1.87%  
Volatility 66.01% 64.64% 74.15%  
Dividend yield 0.00% 0.00% 0.00%  
Stock Option Plan [Member] | Research and Development [Member]        
Share-based Compensation [Abstract]        
Share-based compensation expense $ 668,000 $ 312,000 $ 456,000  
Stock Option Plan [Member] | General and Administrative [Member]        
Share-based Compensation [Abstract]        
Share-based compensation expense 841,000 610,000 1,359,000  
Stock Option Plan [Member] | Sales and Marketing [Member]        
Share-based Compensation [Abstract]        
Share-based compensation expense $ 121,000 $ 0 $ 0  
Stock Option Plan [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Percentage of ownership interest 10.00%      
Percentage of fair market value of common stock 110.00%      
Stock Option Plan [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Term of options 5 years      
Aggregate fair value of common stock $ 100,000      
Period of nontransferable for stock option grants 3 months