Trade Accounts Receivable - Customers Accounted for 10% or More of Trade Accounts Receivable, Net (Detail) - Accounts Receivable [Member] - Credit Concentration Risk [Member]	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Central Banks [Member]
Concentration Risk [Line Items]
Percentage of trade accounts receivable of major customers	51.00%	69.00%
Practical Methods [Member]
Concentration Risk [Line Items]
Percentage of trade accounts receivable of major customers	11.00%	0.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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