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Stock-based Compensation - Additional Information (Detail)
3 Months Ended
Mar. 31, 2018
CompensationPlan
$ / shares
shares
Apr. 20, 2018
shares
Dec. 31, 2008
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of equity compensation plans | CompensationPlan 2    
Common stock available for future grant 421,500    
Weighted average grant date fair value of options granted | $ / shares $ 4.32    
Options to purchase common stock granted 732,212    
2008 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock reserved for issuance 2,473,255   245,884
Rate increase on share reserve 5.00%    
Maximum increase on share reserve 75,000    
Maximum aggregate rate increase on share reserve 25.00%    
Additional shares increased 75,000    
Common stock available for future grant 358,699    
2013 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock available for future grant 62,801    
Excercise price per share | $ / shares $ 6.65    
2013 Plan [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options granted become fully exercisable 2 years    
2013 Plan [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options granted become fully exercisable 4 years    
Share option expiration period 10 years    
2018 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock reserved for issuance 5,000,000 5,000,000  
Performance Option Awards [Member] | Chief Executive Officer [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options to purchase common stock granted 69,000    
Excercise price per share | $ / shares $ 6.55    
Option vesting description Subject to continued service through the vesting date, 1/16 of the awards will vest on each quarterly anniversary of the grant date.    
Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of restricted share units 663,212