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Revenue - Major Customers (Details) - Net Sales - Customer concentration - Two Customers
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Petroleum      
Major Customers and Suppliers      
Concentration risk 26.00% 25.00% 25.00%
Nitrogen Fertilizer      
Major Customers and Suppliers      
Concentration risk 26.00% 28.00% 20.00%