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Revenue Recognition (Narrative) (Details)
T in Millions
Sep. 30, 2020
T
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligations, fixed price contracts (in tons) 16.5
Remaining performance obligations, variable price contracts (in tons) 1.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Remaining performance obligations, fixed price contracts (in tons) 83.6
Remaining performance obligations, variable price contracts (in tons) 5.0