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Investments - Clean Coal Investments - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2022
USD ($)
Entities
Plant
Dec. 31, 2021
USD ($)
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 | Entities 1  
Clean-Coal Investments [Member] | VIE [Member]    
Schedule of Equity Method Investments [Line Items]    
Total assets of limited liability companies $ 35,300,000  
Total liability of limited liability companies $ 35,300,000  
Total revenues of limited liability companies   $ 0
Total expenses of limited liability companies   $ 300,000