Annual report pursuant to Section 13 and 15(d)

Note 1 - Significant Accounting Policies - Percentage of Revenue by Major Customers (Details)

v3.20.4
Note 1 - Significant Accounting Policies - Percentage of Revenue by Major Customers (Details) - Customer Concentration Risk [Member] - Revenue from Contract with Customer Benchmark [Member]
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
BP Products North America [Member]      
Concentration risk percentage 39.00% 40.00% 20.00%
Mercuria Energy America Inc. [Member]      
Concentration risk percentage 10.00%    
Shell Trading (US) Co. [Member]      
Concentration risk percentage   11.00% 30.00%
Vitol Inc. [Member]      
Concentration risk percentage   12.00% 14.00%
Williams Field Services [Member]      
Concentration risk percentage 13.00%