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Postretirement Benefit Plans (Details)
5 Months Ended 7 Months Ended 12 Months Ended
May 31, 2017
USD ($)
Dec. 31, 2019
USD ($)
employee
Dec. 31, 2019
USD ($)
employee
May 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
employee
May 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
employee
Multiemployer Defined Contributory Trust Plan [Member]              
Multiemployer Plans [Line Items]              
Number of employees in plan | employee   1,215 1,215   1,221   1,365
Required employer's contribution per hour per active employee     $ 0.90   $ 0.85   $ 0.80
Required defined contributory trust contribution, percent of earnings     4.50%   4.50%   4.50%
Period Contributions     $ 2,600,000   $ 2,800,000   $ 2,800,000
Multiemployer Health and Welfare Plan [Member]              
Multiemployer Plans [Line Items]              
Number of employees in plan | employee   475 475   604   649
Required employer's contribution per hour per active employee $ 5.80 $ 6.70   $ 6.40   $ 6.10  
Period Contributions     $ 6,700,000   $ 7,700,000   $ 8,100,000