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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 7 Months Ended 12 Months Ended
Jun. 04, 2020
Jun. 04, 2019
Dec. 31, 2020
Jun. 30, 2020
Apr. 30, 2020
Feb. 29, 2020
Dec. 31, 2019
May 31, 2019
Mar. 31, 2019
Sep. 30, 2018
Dec. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2015
Jan. 01, 2021
Nov. 20, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Common stock, par value     $ 0.001       $ 0.001       $ 0.001 $ 0.001 $ 0.001        
Common stock, shares outstanding     49,872,213       46,720,225       49,872,213 49,872,213 46,720,225        
Common stock, shares issued     49,872,213       46,720,225       49,872,213 49,872,213 46,720,225        
Number of options outstanding     5,469,393       4,450,517       5,469,393 5,469,393 4,450,517 4,004,422      
Options granted                       1,377,850          
Incentive Stock Options [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       $ 11,708 $ 10,300 $ 8,401      
Incentive Stock Options [Member] | Research and Development [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       6,765 5,206 3,919      
Incentive Stock Options [Member] | General and Administrative [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       4,943 5,094 4,482      
Director [Member] | Restricted Stock Units [Member] | General and Administrative [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       528 287        
Director [Member] | Share-based Payment Arrangement, Nonemployee [Member] | Restricted Stock Units [Member] | General and Administrative [Member] | June 2019 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       205 287        
Executive Officers [Member] | Restricted Stock Units [Member] | Research and Development [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       1,432 604 476      
Executive Officers [Member] | Restricted Stock Units [Member] | General and Administrative [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       $ 1,167 $ 1,180 $ 1,217      
Consultants [Member] | Share-based Payment Arrangement, Nonemployee [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Options granted                       0 0 0      
Weighted average fair values of outstanding options                           $ 8.74      
Employees And Non-Employee Members Of Board Of Directors [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Fair value of options granted                       $ 10.33 $ 11.67 $ 11.99      
Options granted                       1,377,850 1,324,000 1,197,500      
2019 Inducement Plan [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Common stock, par value                                 $ 0.001
2019 Inducement Plan [Member] | Incentive Stock Options [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Options granted                       0          
2019 Inducement Plan [Member] | Maximum [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Share-based compensation arrangement by share-based payment award, number of shares authorized                                 300,000
2019 Inducement Plan [Member] | Share-based Payment Arrangement, Employee [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Options granted                         47,500        
2019 Inducement Plan [Member] | Share-based Payment Arrangement, Employee [Member] | Share-Based Compensation Award, Tranche One [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Percentage of vested shares on first anniversary of grant date                       25.00%          
2019 Inducement Plan [Member] | Share-based Payment Arrangement, Employee [Member] | Share-based Compensation Award, Tranche Two [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Vesting period of awards granted                       36 months          
2019 Inducement Plan [Member] | Share-based Payment Arrangement, Employee [Member] | Share Based Compensation Subsequent Awards [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Vesting period of awards granted                       4 years          
2014 Equity Incentive Plan [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Number of stock options that may be granted after the tenth anniversary of the 2014 Plan                       0          
Annual increases in number of shares reserved for issuance as a percentage of shares of capital stock outstanding through January 1, 2024                             3.00%    
Share-based compensation arrangement by share-based payment award, number of shares authorized     7,488,513               7,488,513 7,488,513          
2014 Equity Incentive Plan [Member] | Subsequent Event [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Share-based compensation arrangement by share-based payment award, number of shares authorized                               8,984,679  
2014 Equity Incentive Plan [Member] | Maximum [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Term of awards granted                       10 years          
2014 Equity Incentive Plan [Member] | Maximum [Member] | Incentive Stock Options [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Share-based compensation arrangement by share-based payment award, number of shares authorized                             30,000,000    
2014 Equity Incentive Plan [Member] | Director [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Vesting period of awards granted                       3 years          
2014 Equity Incentive Plan [Member] | Director [Member] | Share-based Payment Arrangement, Nonemployee [Member] | Restricted Stock Units [Member] | June 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Vesting period of awards granted 1 year                                
Restricted stock units, approved and granted 36,000                                
Restricted stock units, grant date fair value $ 15.62                                
Restricted stock units vesting date                       Jun. 04, 2021          
Restricted stock units, vested                     0            
2014 Equity Incentive Plan [Member] | Director [Member] | Share-based Payment Arrangement, Nonemployee [Member] | Restricted Stock Units [Member] | June 2019 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Vesting period of awards granted   1 year                              
Restricted stock units, approved and granted   24,000                              
Restricted stock units, grant date fair value   $ 20.47                              
Restricted stock units grant date   Jun. 04, 2019                              
Restricted stock units, vested                       24,000          
2014 Equity Incentive Plan [Member] | Director [Member] | Share-based Payment Arrangement, Nonemployee [Member] | Restricted Stock Units [Member] | General and Administrative [Member] | June 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       $ 323          
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Restricted Stock Units [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Restricted stock units, approved and granted                   83,791              
Common stock, shares issued             36,666 74,166         36,666        
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Restricted Stock Units [Member] | February 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Restricted stock units, vested     36,750                            
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | February 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Restricted stock units, approved and granted           138,000           138,000          
Restricted stock units, grant date fair value           $ 16.36                      
Compensation expense                       $ 601          
Restricted stock units, vested                       36,750          
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | March 2019 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Restricted stock units, approved and granted                 215,000                
Restricted stock units, grant date fair value                 $ 16.10                
Compensation expense                       $ 1,543 $ 1,784        
Restricted stock units, vested       30,000 65,834   36,666 74,166       215,000          
Restricted stock units, Forfeited             8,334                    
Common stock, shares issued       30,000 65,834                        
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | September 2018 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Restricted stock units, approved and granted                   83,791              
Restricted stock units, grant date fair value                   $ 20.21              
Compensation expense                           $ 1,693      
Common stock, shares outstanding                           83,791      
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | Research and Development [Member] | February 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       $ 196          
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | Research and Development [Member] | March 2019 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       1,087 604        
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | Research and Development [Member] | September 2018 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                           $ 476      
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | General and Administrative [Member] | February 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       405          
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | General and Administrative [Member] | March 2019 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       $ 456 $ 1,180        
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Performance Restricted Stock Units [Member] | General and Administrative [Member] | September 2018 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                           $ 1,217      
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | February 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Vesting period of awards granted           3 years                      
Restricted stock units, approved and granted           98,000           98,000          
Restricted stock units, grant date fair value           $ 16.36                      
Compensation expense                       $ 455          
Restricted stock units, vested                       0          
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | Research and Development [Member] | February 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       $ 149          
2014 Equity Incentive Plan [Member] | Executive Officers [Member] | Time-based Restricted Stock Units [Member] | General and Administrative [Member] | February 2020 [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Compensation expense                       $ 306          
2014 Equity Incentive Plan [Member] | Employee And Nonemployee Consultants [Member] | Share-Based Compensation Award, Tranche One [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Percentage of vested shares on first anniversary of grant date                       25.00%          
2014 Equity Incentive Plan [Member] | Employee And Nonemployee Consultants [Member] | Share-based Compensation Award, Tranche Two [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Vesting period of awards granted                       36 months          
2014 Equity Incentive Plan [Member] | Employee And Nonemployee Consultants [Member] | Share Based Compensation Subsequent Awards [Member]                                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Vesting period of awards granted                       4 years