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Summary of Significant Accounting Policies - Additional Information (Detail) | 3 Months Ended
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Mar. 31, 2018 Country Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Number of reportable operating segments | Segment | 3
Number of commercial clean coal production facilities | 34
Number of countries in which the company has operations | 33
Number of countries in which the company does business through a network of correspondent brokers and consultants | 150
Description of contracts renewal period | One year or less
Percentage of commission and fee revenues on the effective date | 70.00%
Percentage of commission and fee revenues in the first three months | 20.00%
Percentage of commission and fee revenues after the first three months | 10.00%

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