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Employee Benefits - Contributions to Multiemployer Pensions and Health and Welfare Benefit Plans (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Multiemployer Plan [Line Items]      
Total contributions $ 2,080 $ 1,483 $ 1,595
Pension plans      
Multiemployer Plan [Line Items]      
Total contributions 1,128 809 871
Health & welfare plans      
Multiemployer Plan [Line Items]      
Total contributions $ 952 $ 674 $ 724