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Stockholders' Equity - Employee Stock Purchase Plan (Details) - USD ($)
$ in Thousands
12 Months Ended
Feb. 27, 2018
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares available for grant (in shares)   2,300,000
Employee Stock Purchase Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Purchase price of common stock, percent 85.00%  
Maximum purchase value during offering period, per employee $ 15  
Employee Stock Purchase Plan | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Percentage of purchase value during offering period, per employee 0.00%  
Employee Stock Purchase Plan | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Percentage of purchase value during offering period, per employee 10.00%  
Common Stock | Employee Stock Purchase Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares available for grant (in shares) 500,000  
Shares issued in period (in shares)   0