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Post Retirement Benefits - Multiemployer Plans (Details)
 12 Months Ended
Aug. 10, 2019
$ / h
Aug. 05, 2018
$ / h
Dec. 31, 2017
USD ($)
Aug. 06, 2017
$ / h
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Multiemployer plans:            
Certified zone status, percent funded limit for red status     65.00%      
Certified zone status, percent funded limit for yellow status     80.00%      
Certified zone status, percent funded limit for green status     80.00%      
Multi-employer plan contributions | $ [1]     $ 647,000   $ 710,000 $ 863,000
Multiemployer plan, postretirement benefit            
Multiemployer plans:            
Maximum percentage of total contribution     5.00%      
Multiemployer plans, collective-bargaining arrangement, maximum hours of work per week for employer contribution     40 hours      
Multiemployer plans, collective-bargaining arrangement, rate of employer contribution       1.45    
Forecast | Multiemployer plan, postretirement benefit            
Multiemployer plans:            
Multiemployer plans, collective-bargaining arrangement, rate of employer contribution 1.55 1.50        
[1] The plan re-certified its zone status after using the amortization provisions of the Code. The Company's contributions to the plan did not represent more than 5% of total contributions to the plan as indicated in the plan's most recently available annual report for the plan year ended December 31, 2016. Under the terms of the collective-bargaining agreement, the Company is required to make contributions to the plan for each hour worked up to a maximum of 40 hours per person, per week, at the following rates: $1.45 per hour from August 8, 2016 through August 6, 2017; $1.50 per hour from August 7, 2017 through August 5, 2018; $1.55 per hour from August 6, 2018 through August 10, 2019.