Commitments and Contingencies - Collective Bargaining Agreements and Environmental Contingencies (Details)	12 Months Ended
	Dec. 31, 2019 employee location item
Employees covered by collective bargaining agreements
Collective Bargaining Agreements
Number of Location Entity Operates | location	52
Total employees | Employees covered by collective bargaining agreements
Collective Bargaining Agreements
Percentage of employees covered by collective bargaining agreements	11.00%
Number of employees | employee	1,690
Number of collective bargaining agreements that expire over the next six years | item	62
Expiration period of collective bargaining agreements	6 years
Employees covered by collective bargaining agreements that expire during 2020
Collective Bargaining Agreements
Number of employees | employee	400
Number of collective bargaining agreements that expire within one year | item	18