Revenue Recognition (Narrative) (Details) T in Millions	Jun. 30, 2021 T
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, fixed price contracts (in tons)	31.3
Remaining performance obligations, variable price contracts (in tons)	4.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, fixed price contracts (in tons)	52.9
Remaining performance obligations, variable price contracts (in tons)	1.3