Note 6 - Property, Plant and Equipment - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Property, plant and equipment, gross	$ 310,490	$ 302,270
Accumulated depreciation	(204,101)	(197,561)
Property, plant and equipment, net	106,389	104,709
Land [Member]
Property, plant and equipment, gross	21,826	21,826
Land Improvements [Member]
Property, plant and equipment, gross	$ 5,125	$ 5,024
Land Improvements [Member] \| Minimum [Member]
Estimated Useful Lives (Year)	10 years
Land Improvements [Member] \| Maximum [Member]
Estimated Useful Lives (Year)		20 years
Storage and Terminal Facilities [Member]
Property, plant and equipment, gross	$ 257,433	$ 249,977
Storage and Terminal Facilities [Member] \| Minimum [Member]
Estimated Useful Lives (Year)	10 years
Storage and Terminal Facilities [Member] \| Maximum [Member]
Estimated Useful Lives (Year)		35 years
Office Equipment [Member]
Property, plant and equipment, gross	$ 21,751	$ 23,278
Office Equipment [Member] \| Minimum [Member]
Estimated Useful Lives (Year)	3 years
Office Equipment [Member] \| Maximum [Member]
Estimated Useful Lives (Year)		30 years
Construction in Progress [Member]
Property, plant and equipment, gross	$ 4,355	$ 2,165

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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