Note 7 - Affiliate Balances - Company Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues of Angolan operations (in thousands)	$ 86,467	$ 119,765	$ 305,179	$ 367,772
Sonatide [Member] | ANGOLA
Revenues of Angolan operations (in thousands)	$ 10,660	$ 11,534	$ 35,086	$ 41,194
Percent of consolidated vessel revenues	12.00%	10.00%	12.00%	11.00%
Number of company owned vessels in Angola	24	31	26	33
Number of stacked company owned vessels in Angola	8	14	9	14