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Investments - Clean Coal Investments - Additional Information (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2021
USD ($)
Entity
Plant
Chem-Mod LLC [Member]  
Schedule of Equity Method Investments [Line Items]  
Number of clean coal production plants owned | Plant 35
Chem-Mod LLC [Member] | 2009 Era Plants [Member]  
Schedule of Equity Method Investments [Line Items]  
Number of clean coal production plants owned | Plant 14
Chem-Mod LLC [Member] | 2011 Era Plants [Member]  
Schedule of Equity Method Investments [Line Items]  
Number of clean coal production plants owned | Plant 21
Clean-Coal Investments [Member]  
Schedule of Equity Method Investments [Line Items]  
Number of variable interest entities | Entity 1
Clean-Coal Investments [Member] | VIE [Member]  
Schedule of Equity Method Investments [Line Items]  
Total assets of limited liability companies $ 41.7
Total liability of limited liability companies 41.7
Total revenues of limited liability companies 86.1
Total expenses of limited liability companies $ 104.6