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Stock-Based Compensation - Stock Options Plans (Details) - USD ($)
3 Months Ended
Jan. 01, 2020
Jan. 01, 2019
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Jun. 26, 2018
Jun. 13, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares reserves available future issuance (in shares)     6,108,917   4,918,150    
Stock-based compensation expense     $ 1,669,000 $ 1,729,000      
2015 Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares reserves available future issuance (in shares)     0   0 0  
2018 Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares reserves available future issuance (in shares)     395,741        
Total number of shares authorized for issuance (in shares)             1,215,000
Annual increase as a percentage of common stock outstanding (in percent)     4.00%        
Number of additional shares authorized (in shares) 1,149,189 1,132,570          
ESPP              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Total number of shares authorized for issuance (in shares)             270,000
Number of additional shares authorized (in shares) 287,297 283,142          
Shares issued (in shares)       62,927      
Shares reserved and available for issuance (in shares)         777,512    
Stock-based compensation expense     $ 0 $ 0      
ESPP | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Annual increase as a percentage of common stock outstanding (in percent)     1.00%        
Annual increase to common stock (in shares)     405,000