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Summary of Significant Accounting Policies - Additional Information (Detail)	6 Months Ended
	Jun. 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	35
Number of countries in which the company does business through a network of correspondent brokers and consultants	150