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Post-Retirement Plan (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Post-Retirement Plan [Abstract]      
Matching contribution, percentage 50.00% 50.00% 50.00%
Employer contribution, percet of employee's gross pay 6.00% 6.00% 6.00%
Contribution, amount $ 2.5 $ 1.9 $ 1.9