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Summary of Significant Accounting Policies - Additional Information (Detail)
 9 Months Ended
Sep. 30, 2019
Country
Segment
Significant Accounting Policies [Line Items]  
Number of reportable operating segments | Segment 3
Number of commercial clean coal production facilities 34
Number of countries in which the company has operations 48
Number of countries in which the company does business through a network of correspondent brokers and consultants 150