Note 15 - Selected Quarterly Financial Information (Unaudited) - Schedule of Selected Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2020	[1]	Sep. 30, 2020	[1]	Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019	[1]	Sep. 30, 2019	[1]	Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2020	Dec. 31, 2019
General and administrative expense	$ 1,631		$ 2,275		$ 2,028		$ 3,532		$ 2,060		$ 2,262		$ 2,603		$ 3,057		$ 9,466	$ 9,982
Operating loss	(1,631)		(2,275)		(2,028)		(3,532)		(2,060)		(2,262)		(2,603)		(3,057)		(9,466)	(9,982)
Other income (loss), net	(663)		(820)		(2,658)		(3,567)		2,245		8,777		3,118		(1,885)		(7,708)	12,255
Interest income	52		52		52		105		174		234		763		873		261	2,044
Equity income (loss), net	(5,111)		(1,300)		(5,277)		(9,014)		(1,057)		(3,440)		40,497		28,267		(20,702)	64,267
Net loss before income taxes	(7,353)		(4,343)		(9,911)		(16,008)		(698)		(2,497)		36,093		21,663		(37,615)	54,561
Net income (loss)	$ (7,353)		$ (4,343)		$ (9,911)		$ (16,008)		$ (698)		$ (2,497)		$ 36,093		$ 21,663		$ (37,615)	$ 54,561
Basic (in dollars per share)	$ (0.35)	[2]	$ (0.21)	[2]	$ (0.48)	[2]	$ (0.77)	[2]	$ (0.03)	[2]	$ (0.12)	[2]	$ 1.75	[2]	$ 1.05	[2]	$ (1.81)	$ 2.64
Diluted (in dollars per share)	$ (0.35)	[2]	$ (0.21)	[2]	$ (0.48)	[2]	$ (0.77)	[2]	$ (0.03)	[2]	$ (0.12)	[2]	$ 1.75	[2]	$ 1.05	[2]	$ (1.81)	$ 2.64
Interest expense											$ 5,806		$ 5,682		$ 2,535		$ (0)	$ 14,023

[1] The three months ended December 31, 2019 includes equity income of $1.4 million related to an equity method investment that should have been recorded during the three months ended September 30, 2019. There was no impact on the full year results.

[2] Per share amounts for the quarters have each been calculated separately. Accordingly, quarterly amounts may not add to the annual amounts because of differences in the average common shares outstanding during each period. Additionally, in regard to diluted per share amounts only, quarterly amounts may not add to the annual amounts because of the inclusion of the effect of potentially dilutive securities only in the periods in which such effect would have been dilutive, and because of the adjustments to net income (loss) for the dilutive effect of common stock equivalents and convertible securities at our ownership interests.