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Retirement and Share-based Compensation Plans (Defined Contribution Plan) (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Payment Arrangement [Abstract]      
Defined contribution plan, maximum annual employee contribution $ 19,000 $ 18,500 $ 18,000
Defined contribution plan, employer plan contributions $ 1,800,000 $ 1,700,000 $ 1,400,000