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Company Retirement Plans (Details) - United States - 401(k) Plan - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Company retirement plans      
Employer discretionary contributions $ 0 $ 0 $ 0
Employer's contribution $ 7,000 $ 4,600 $ 4,200