Trade Accounts Receivable - Customers Accounted for 10% or More of Trade Accounts Receivable, Net (Detail)	6 Months Ended	12 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Accounts Receivable [Member] \| Credit Concentration Risk [Member] \| Central Banks [Member]
Concentration Risk [Line Items]
Percentage of trade accounts receivable of major customers	55.00%	48.00%

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration