Note 8 - Asset Held for Sale, Asset Sales and Asset Impairments - Summary of Vessel Sales and Gains on Sales of Vessels (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Gain on sale of vessels	$ 7,591	$ 2,263	$ 10,624
Vessels sold from assets held for sale	53
Vessels Held for Sale [Member]
Gain on sale of vessels	$ 6,384	$ 0	$ 0
Vessels sold from assets held for sale	53	(0)	(0)
Vessels, Active Fleet [Member]
Vessels sold from active fleet	3	40	38
Gain on sale of vessels	$ 1,217	$ 2,434	$ 10,935
Vessel [Member]
Gain on sale of vessels	$ 7,601	$ 2,434	$ 10,935
Total vessels sold	56	40	38

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, excluding oil and gas property and timber property.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

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