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Pension Plans - Multi-employer (Details) - Multi-employer defined benefit pension plan - USD ($)
$ in Thousands
1 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2012
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Pension Plans            
Insolvent period   20 years        
Estimated liability upon withdrawal from plan       $ 99,800 $ 81,600 $ 82,200
Percentage of annual compounded surcharge for rehabilitation   5.00%        
Percentage of interim surcharge 5.00%          
Pension expense   $ 1,504 $ 1,548 2,961 2,836  
Surcharges   $ 530 $ 496 $ 948 $ 811