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Note 12 - Related-Party Transactions (Details Textual) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 30, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Due from Related Parties, Current, Total		$ 1,043	$ 1,110	$ 1,043
Payments to Acquire Property, Plant, and Equipment, Total			12,746	34,400
Tangible Asset Impairment Charges, Total			274	42,860
Other than Temporary Impairment Losses, Investments, Total			2,202	10,019
Equity Method Investments			0
Cimarron Express [Member]
Other than Temporary Impairment Losses, Investments, Total			2,200	10,000
Interest Costs Capitalized			2,000
Ergon [Member]
Equity Method Investments			$ 10,200
Ergon [Member] \| Cimarron Express [Member]
Other than Temporary Impairment Losses, Investments, Total				10,000
Ergon [Member] \| Cimarron Express [Member]
Noncontrolling Interest, Ownership Percentage by Parent			50.00%
Cimarron Express [Member]
Payments to Acquire Property, Plant, and Equipment, Total				30,600
Tangible Asset Impairment Charges, Total		20,900
Gain (Loss) on Disposition of Assets, Total	$ 1,400
Ergon [Member]
Revenue from Related Parties			$ 36,200	48,500
Due from Related Parties, Current, Total		$ 1,000	1,100	1,000
Ergon [Member] \| Crude Oil Purchase Agreement [Member]
Related Party Transaction, Purchases from Related Party			133,500	108,800
Accounts Payable, Related Parties			11,800
Ergon [Member] \| Ergon 2017 Lubbock and Saginaw Storage and Handling Agreement [Member]
Revenue from Related Parties				6,700
Ergon [Member] \| Ergon 2016 Storage and Handling Agreement [Member]
Revenue from Related Parties			20,000	24,800
Ergon [Member] \| Ergon Fontana and Las Vegas Storage Throughput and Handling Agreement [Member]
Revenue from Related Parties			6,000	6,600
Ergon [Member] \| Ergon Lessee Operated Facility Lease Agreement [Member]
Operating Lease, Lease Income, Total			$ 8,300
Ergon [Member] \| Ergon Master Facilities Lease and Sublease Agreement [Member]
Operating Lease, Lease Income, Total				5,300
Ergon [Member] \| Ergon Master Facilities Sublease and Sublicense Agreement [Member]
Operating Lease, Lease Income, Total				$ 2,800