Note 7 - Affiliates Balances - Company Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues of Angolan operations (in thousands)	$ 92,401	$ 86,467	$ 265,858	$ 305,179
Sonatide [Member] | ANGOLA
Revenues of Angolan operations (in thousands)	$ 12,046	$ 10,660	$ 30,413	$ 35,086
Percent of consolidated vessel revenues	13.00%	12.00%	11.00%	12.00%
Number of company owned vessels in Angola	24	24	23	26
Number of stacked company owned vessels in Angola	4	8	5	9