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
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Summary Of Significant Accounting Policies - Major Customers And Concentration Of Risk (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Petrobras
Revenue, Major Customer [Line Items]
Percentage of concentration risk	28.00%	29.00%	28.00%
BP
Revenue, Major Customer [Line Items]
Percentage of concentration risk	17.00%	15.00%	15.00%
Shell
Revenue, Major Customer [Line Items]
Percentage of concentration risk		13.00%