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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Jun. 16, 2016
Dec. 03, 2014
Oct. 31, 2014
Jul. 31, 2012
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unrecognized compensation cost related to outstanding options           $ 2,600 $ 3,900  
Intrinsic value of options exercised           $ 10 300  
Weighted average grant date fair value of vested options           $ 4.71    
Weighted average grant date fair value of options outstanding           $ 3.67    
Stock-based compensation expense           $ 1,548 1,228  
2012 Equity Incentive Plan [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares authorized for issuance               609,389
Stock options vesting period       3 years        
Term of stock options granted       10 years        
2012 Equity Incentive Plan [Member] | First Anniversary of Original Vesting Date [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock options vesting percentage       25.00%        
2013 Equity Incentive Plan [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock options vesting period     3 years          
Term of stock options granted     10 years          
2013 Equity Incentive Plan [Member] | First Anniversary of Original Vesting Date [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock options vesting percentage     25.00%          
2013 Equity Incentive Plan [Member] | EIP Amendment [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Increase in authorized shares of common stock amount 300,000              
Increase in authorized shares, percentage of common stock outstanding     4.00%          
2013 Employee Stock Purchase Plan [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares authorized for issuance   103,665            
Increase in authorized shares of common stock amount   51,832            
Increase in authorized shares, percentage of common stock outstanding   1.00%            
General and Administrative [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation expense           1,057 777  
Restricted stock-based compensation expense           $ 2 $ 4  
Scenario, Forecast [Member] | 2013 Equity Incentive Plan [Member] | EIP Amendment [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Increase in authorized shares of common stock amount         825,904      
Scenario, Forecast [Member] | 2013 Employee Stock Purchase Plan [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Increase in authorized shares of common stock amount         206,476      
Stock Options [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unrecognized compensation cost, recognition period           2 years 4 days 2 years 8 months 5 days  
Restricted Stock [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unrecognized compensation cost, recognition period           3 months 18 days 1 year 2 months 12 days  
Unrecognized compensation cost related to restricted stock awards           $ 1 $ 4