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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended
Sep. 02, 2015
Sep. 30, 2015
Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate     1.76%
Expected term     6 years
Expected volatility     72.98%
Dividend yield     0.00%
Weighted average grant-date fair value of stock options granted   $ 4.91 $ 4.06
Unvested service-based stock options held by nonemployees   3,934 3,934
Total unrecognized compensation cost related to the unvested awards   $ 5,108 $ 5,108
Unrecognized compensation cost related to the unvested awards, weighted-average period     3 years 6 months
Restricted Common Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total fair value of restricted common stock vested     $ 295
2013 Stock Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of estimated fair value of the shares on the date of grant     100.00%
Stock options expiration period     10 years
Common stock reserved for issuance   3,520,396 3,520,396
Common stock reserved for future grant   54,510 54,510
2013 Stock Plan [Member] | Employees And Directors [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock options vesting period     4 years
2013 Stock Plan [Member] | Non Employees [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock options vesting period     2 years
2013 Stock Plan [Member] | Non Employees [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock options vesting period     4 years
2013 Stock Plan [Member] | Restricted Common Stock [Member] | Employees And Directors [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted in connection with employee stock purchase plan     35,788
2013 Stock Plan [Member] | Options to Purchase Common Stock [Member] | Employees And Directors [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted in connection with employee stock purchase plan     1,938,705
2015 Stock Option and Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock reserved for issuance 1,422,886    
Common stock reserved for issuance, percentage of number of shares of common stock outstanding 4.00%    
2015 Employee Stock Purchase Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock reserved for issuance 256,585    
Common stock reserved for issuance, percentage of number of shares of common stock outstanding 1.00%    
2015 Employee Stock Purchase Plan [Member] | Non Employees [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted in connection with employee stock purchase plan     0