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Stockholders' Equity - Additional Information (Details)
1 Months Ended 12 Months Ended
Apr. 30, 2016
shares
Jan. 31, 2010
USD ($)
shares
Dec. 31, 2017
USD ($)
installment
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Stock based compensation expense | $     $ 700,000 $ 900,000
Stock-based compensation expense expected to be recognized | $     $ 500,000  
Carilion Clinic        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Senior convertible Promissory Notes principal amount converted | $   $ 5,000,000.0    
Accrued interest converted | $   $ 1,200,000    
Percentage of dividend payable on series A convertible preferred stock   6.00%    
Preferred stock liquidation preference value | $   $ 6,200,000    
Shares of common stock dividends (in shares)     631,693  
Unexercised warrants (in shares)     366,000  
Exercise price of warrants (in dollars per share) | $ / shares     $ 2.50  
Carilion Clinic | Series A Convertible Preferred Stock        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Preferred stock issued in exchange of notes payable (in shares)   1,321,514    
Stock Options        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Vesting period     4 years  
Weighted average grant date fair value of options granted (in dollars per share) | $ / shares     $ 1.18 $ 1.15
Weighted average remaining service period       3 years 2 months 12 days
Stock Options | Carilion Clinic        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Conversion of stock, ratio   1    
Restricted Stock        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Shares issued (in shares)     349,000 319,000
Share-based compensation vesting installments | installment     3  
Shares vested (in shares)     530,542 245,583
Restricted Stock Units (RSUs) | Member of Board of Directors        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Shares issued (in shares)     129,865 86,956
Shares vested (in shares)     86,956 48,542
2016 Equity Incentive Plan        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Shares available for future grant (in shares) 3,500,000      
Stock option contractual term 10 years