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401(K) Plan and Other Defined Contribution Plans (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
The 401(K) Plan      
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan, matching contribution, percent of employee's base salary 3.00%    
Defined contribution plan, cost $ 1,400 $ 1,400 $ 1,400
Defined contribution plan, employer discretionary contribution amount 1,800 1,800 1,500
EDCP      
Defined Contribution Plan Disclosure [Line Items]      
Compensation expense $ 237 $ 298 $ 441