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Postretirement Benefit Plans (Details) - Multiemployer Health and Welfare Plan [Member]
 12 Months Ended 17 Months Ended 19 Months Ended
Dec. 31, 2016
USD ($)
employee
Dec. 31, 2015
USD ($)
employee
May 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
employee
May 31, 2014
USD ($)
Dec. 31, 2016
USD ($)
employee
Multiemployer Plans [Line Items]            
Number of employees in plan | employee 658 651   652   658
Required employer's contribution per hour per active employee     $ 5.25   $ 5.00 $ 5.50
Period Contributions $ 7,600,000 $ 7,600,000   $ 7,300,000