Note 7 - Leases (Details Textual) $ in Thousands	Mar. 06, 2019 USD ($) a	Dec. 31, 2020 USD ($) a	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Jan. 31, 2017 a
Operating Lease, Liability, Total		$ 432	$ 701
Operating Lease, Right-of-Use Asset		429	1,054
Retained Earnings (Accumulated Deficit), Ending Balance		$ (148,030)	$ (133,701)
Accounting Standards Update 2016-02 [Member]
Operating Lease, Liability, Total				$ 1,900
Operating Lease, Right-of-Use Asset				1,600
Deferred Rent Credit				(100)
Accounting Standards Update 2016-02 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Retained Earnings (Accumulated Deficit), Ending Balance				$ (200)
BND [Member]
Area Available for Lease (Acre) | a	984
Lessee, Operating Lease, Term of Contract (Year)	30 years
Lessee, Operating Lease, Number of Consecutive Renewal Term	2
Lessee, Operating Lease, Renewal Term (Year)	10 years
Operating Lease, Liability, Total	$ 2,300
City of Texas City and the State of Texas [Member]
Area Available for Lease (Acre) | a					994
Lessee, Operating Lease, Term of Contract (Year)					36 months
Lessee, Operating Lease, Renewal Term (Year)					12 months
Houston, Texas [Member]
Area of Real Estate Property (Acre) | a		25,600