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Stock-Based Compensation - Additional Information (Detail)
9 Months Ended
Sep. 30, 2018
USD ($)
Period
$ / shares
shares
Sep. 30, 2017
shares
Apr. 28, 2015
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Cash proceeds from exercises of stock options | $ $ 396,000    
Option exercises 171,567 0  
Weighted average fair value of stock options granted to employees | $ / shares $ 4.11    
Excess tax benefit from stock-based awards | $ $ 0    
2014 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares of common stock reserved for issuance     1,527,770
Additional number of shares of common stock reserved for issuance 2,321,363    
Common stock reserved for issuance, description Initially, a total of 1,527,770 shares of the Company’s common stock were reserved for issuance pursuant to the 2014 Plan, which number is also the limit on shares of common stock available for awards of incentive stock options. The number of shares available for issuance under the 2014 Plan will, unless otherwise determined by the Company’s Board of Directors or the Compensation Committee, be automatically increased on January 1st of each year commencing on January 1, 2016 and ending on (and including) January 1, 2024, in an amount equal to 3.5% of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year.    
Percentage of common stock outstanding to increase shares reserved for issuance 3.50%    
2014 ESPP [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares of common stock reserved for issuance     458,331
Additional number of shares of common stock reserved for issuance 663,246    
Common stock reserved for issuance, description The number of shares available for issuance under the ESPP will, unless otherwise determined by the Company’s Board of Directors or the Compensation Committee, be automatically increased on January 1st of each year commencing on January 1, 2016 and ending on (and including) January 1, 2024, in an amount equal to 1% of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year.    
Percentage of common stock outstanding to increase shares reserved for issuance 1.00%    
Duration of employee stock purchase plan as determined by the compensation committee 24 months    
Duration for offering period, employee stock purchase plan 6 months    
Employee stock purchase plan, number of purchase periods | Period 4    
Maximum duration for purchase under employee stock purchase plan 1 year    
Maximum duration of employee stock purchase plan 27 months    
Percentage of purchase of common stock 85.00%    
Percentage of common stock on the date of purchase 85.00%