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Employee Benefits - 401(k) and profit sharing plan (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
401(k) plan      
Schedule of Defined Contribution Plans Disclosures [Line Items]      
Requisite service period 1 month    
Employer contribution amount $ 1,008 $ 959 $ 748
Profit sharing plan      
Schedule of Defined Contribution Plans Disclosures [Line Items]      
Requisite service period 2 years    
Percentage vesting annually 100.00%    
Employer contribution amount $ 370 $ 750 $ 900
Minimum | 401(k) plan      
Schedule of Defined Contribution Plans Disclosures [Line Items]      
Employer matching of employee contributions, percentage 50.00%    
Employer matching contribution, percentage of compensation 3.00%    
Maximum | 401(k) plan      
Schedule of Defined Contribution Plans Disclosures [Line Items]      
Employer matching of employee contributions, percentage   100.00%  
Employer matching contribution, percentage of compensation 5.00%