Major Customers - Narrative (Details)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valero energy corporation
Revenue, Major Customer [Line Items]
Concentration risk, percentage	17.00%	12.00%	10.00%

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.

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