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Intangible Assets (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Finite-Lived Intangible Assets, Net [Abstract]    
Net Balance $ 31,774 $ 35,330
Amortization of intangible assets 3,556 2,572
Expected annual amortization expense, 2022 3,100  
Expected annual amortization expense, 2023 3,100  
Expected annual amortization expense, 2024 3,100  
Expected annual amortization expense, 2025 3,100  
Expected annual amortization expense, 2026 3,100  
Coal supply agreement    
Finite-Lived Intangible Assets, Net [Abstract]    
Gross Carrying Amount 84,200 84,200
Accumulated Amortization (52,426) (48,870)
Net Balance $ 31,774 $ 35,330