Investments - Clean Coal Investments - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2023 USD ($) Entities 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 | Entities	1
Clean-Coal Investments [Member] | VIE [Member]
Schedule of Equity Method Investments [Line Items]
Total assets of limited liability companies	$ 34,500,000
Total liability of limited liability companies	34,300,000
Total revenues of limited liability companies	0
Total expenses of limited liability companies	$ (100,000)