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Pension and Post-Retirement Benefits - Additional Information (Details)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
plan
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
plan
Jun. 30, 2017
USD ($)
Defined Benefit Plan Disclosure        
Number of multiemployer plans | plan 3   3  
Multiemployer plan, percentage of fund's total contributions     5.00%  
Pension Benefits        
Defined Benefit Plan Disclosure        
Contributions to plan by employer $ 0.5 $ 0.3 $ 0.8 $ 0.3
Expected contributions in current fiscal year 2.5   2.5  
Post-retirement Benefits        
Defined Benefit Plan Disclosure        
Expected contributions in current fiscal year $ 1.4   $ 1.4