Annual report pursuant to Section 13 and 15(d)

Note 15 - Commitments (Details Textual)

v3.20.4
Note 15 - Commitments (Details Textual) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Expense Relating to Surety Bonds Paid. $ 5,400 $ 4,700 $ 5,900
Surety Bonds [Member]      
Other Commitment, to be Paid, Year One 5,800    
Other Commitment, to be Paid, Year Two 5,600    
Other Commitment, to be Paid, Year Three 5,700    
Other Commitment, to be Paid, Year Four 5,600    
Other Commitment, to be Paid, Year Five 5,600    
Other Commitment, Due after Fifth Year 57,900    
Surety Bonds [Member] | Other Commitment [Member]      
Bonding Requirement, Related To Purchase of Properties Minimum Amount 64,000    
Bonding Requirement Related To Purchase of Properties Maximum Amount 94,000    
Surety Bonds [Member] | Total E&P [Member]      
Bonding Requirement Related to Purchase of Properties Amount Current Year. 93,700    
Escrow Deposit 0    
Bonding Requirement Related to Purchase of Properties Amount, Fifth Anniversary. 103,000    
Bonding Requirement Related to Purchase of Properties Amount Increment From Second Anniversary. 3,000    
Surety Bonds [Member] | Exxon [Member]      
Bonding Requirement, Related To Purchase of Properties Minimum Amount 30,000    
Other Commitment, to be Paid, Year One 33,000    
Other Commitment, to be Paid, Year Two 36,300    
Other Commitment, to be Paid, Year Three 40,000    
Other Commitment, to be Paid, Year Four 44,000    
Other Commitment, to be Paid, Year Five 48,300    
Other Commitment, Due after Fifth Year 114,000    
Surety Bonds [Member] | Exxon [Member] | Minimum [Member]      
Annual Increase in Other Commitment 4,000    
Surety Bonds [Member] | Exxon [Member] | Maximum [Member]      
Annual Increase in Other Commitment 9,000    
Surety Bonds [Member] | Conoco [Member]      
Bonding Requirement, Related To Purchase of Properties Minimum Amount 49,000    
Heidelberg Field [Member]      
Other Commitment, to be Paid, Year One 2,500    
Other Commitment, to be Paid, Year Two 1,800    
Other Commitment, to be Paid, Year Three 1,200    
Other Commitment, to be Paid, Year Four 800    
Other Commitment, to be Paid, Year Five 600    
Other Commitment, Due after Fifth Year 700    
Other Commitment, Expense $ 4,500 $ 4,500 $ 2,300