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Stock Incentive Plans - Narrative (Details)
$ / shares in Units, $ in Thousands
3 Months Ended
Jun. 21, 2016
shares
Mar. 31, 2020
USD ($)
$ / shares
shares
Mar. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2019
shares
Mar. 25, 2019
shares
Sep. 25, 2018
shares
Dec. 31, 2008
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Common stock authorized and reserved for future issuance (in shares)   44,390,813   40,169,185      
Employee stock option grants              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Common stock authorized and reserved for future issuance (in shares)   5,048,316   1,765,018      
Estimated forfeitures rate   10.00%          
Weighted average grant date fair value of stock options (in dollars per share) | $ / shares   $ 1.69 $ 1.77        
Aggregate intrinsic value of stock options exercised | $   $ 100 $ 100        
Unrecognized compensation expense related to unvested employee stock options | $   $ 10,200          
Weighted average period for recognition   2 years 6 months          
Non-employee stock options              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Unrecognized compensation expense related to unvested non-employee stock options | $   $ 100          
Unrecognized compensation expense related to unvested non-employee stock options, period   2 months 12 days          
Unvested restricted stock units              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Common stock authorized and reserved for future issuance (in shares)   170,313   181,250      
Grants in period (in shares)   0          
Vested in period (in dollars per share) | $ / shares   $ 6.03          
Grants in period (in dollars per share) | $ / shares   $ 0          
The 2008 Plan and the 2016 Plan | Employee stock option grants              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Issuance of common stock upon exercise of options (in shares)   5,128          
Aggregate intrinsic value of stock options exercised | $   $ 1,541          
The 2008 Plan and the 2016 Plan | Non-employee stock options              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Issuance of common stock upon exercise of options (in shares)   0          
Aggregate intrinsic value of stock options exercised | $   $ 40          
2008 Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares authorized for grants (in shares)             2,213,412
2008 Plan | Employee stock option grants              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Award vesting term   4 years          
Award expiration term   10 years          
2016 Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares authorized for grants (in shares)   1,210,256          
Automatic increase in the number of shares that may be issued (as a percent)   0.04          
Number of shares authorized, increase (in shares)   3,453,022 898,871        
Common stock authorized and reserved for future issuance (in shares)   2,416,239          
2016 Plan | Employee stock option grants              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Award vesting term   4 years          
Award expiration term   10 years          
2016 Plan | Employee stock option grants | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Combined voting power of participants (as a percent)   10.00%          
2016 Plan | Employee stock option grants | Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Combined voting power of participants (as a percent)   10.00%          
2016 Plan | Employee stock option grants | Tranche One | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of incentive stock options (not less than)   100.00%          
2016 Plan | Employee stock option grants | Tranche Two | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of incentive stock options (not less than)   110.00%          
Employment Inducement Incentive Award Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares authorized for grants (in shares)   1,100,000          
Common stock authorized and reserved for future issuance (in shares)         2,000,000 1,175,000  
Employment Inducement Incentive Award Plan | Unvested restricted stock units              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Weighted average period for recognition   2 years 7 months 6 days          
Unrecognized compensation expense | $   $ 700          
ESPP              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Automatic increase in the number of shares that may be issued (as a percent) 0.01            
Number of shares authorized, increase (in shares)   863,254 224,717        
Common stock authorized and reserved for future issuance (in shares) 173,076 1,532,077          
Exercise price of incentive stock options (not less than) 85.00%