Note 5 - Property, Plant and Equipment - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Property, plant and equipment, gross	$ 517,586	$ 511,815
Accumulated depreciation	(278,768)	(263,554)
Property, plant and equipment, net	238,818	248,261
Land [Member]
Property, plant and equipment, gross	24,705	24,705
Land Improvements [Member]
Property, plant and equipment, gross	$ 5,804	5,758
Land Improvements [Member] \| Minimum [Member]
Estimated Useful Lives (Year)	10 years
Land Improvements [Member] \| Maximum [Member]
Estimated Useful Lives (Year)	20 years
Pipelines [Member]
Property, plant and equipment, gross	$ 118,449	116,155
Pipelines [Member] \| Minimum [Member]
Estimated Useful Lives (Year)	5 years
Pipelines [Member] \| Maximum [Member]
Estimated Useful Lives (Year)	30 years
Storage and Terminal Facilities [Member]
Property, plant and equipment, gross	$ 326,738	321,096
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
Transportation Equipment [Member]
Property, plant and equipment, gross	$ 3,140	2,798
Transportation Equipment [Member] \| Minimum [Member]
Estimated Useful Lives (Year)	3 years
Transportation Equipment [Member] \| Maximum [Member]
Estimated Useful Lives (Year)	10 years
Office Equipment [Member]
Property, plant and equipment, gross	$ 27,415	26,980
Office Equipment [Member] \| Minimum [Member]
Estimated Useful Lives (Year)	3 years
Office Equipment [Member] \| Maximum [Member]
Estimated Useful Lives (Year)	20 years
Pipeline Linefill and Tank Bottoms [Member]
Property, plant and equipment, gross	$ 8,258	10,297
Construction in Progress [Member]
Property, plant and equipment, gross	$ 3,077	$ 4,026

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