Note 5 - Leases (Details Textual) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) ft² a	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 31, 2017 a
Operating Lease, Liability, Total	$ 1,522
Operating Lease, Right-of-Use Asset	$ 1,336
Accounting Standards Update 2016-02 [Member]
Operating Lease, Liability, Total		$ 1,900
Operating Lease, Right-of-Use Asset		1,600
Deferred Rent Credit		(100)
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 200	$ (213)
City of Texas City and the State of Texas [Member]
Area Available for Lease | a				994
Lessee, Operating Lease, Term of Contract	3 years
Lessee, Operating Lease, Renewal Term	1 year
BND [Member]
Area Available for Lease | a	984
Lessee, Operating Lease, Term of Contract	30 years
Lessee, Operating Lease, Renewal Term	10 years
Maximum Period for Automatic Extension for Outside Effective Date	180 days
Lessee, Operating Lease, Number of Consecutive Renewal Term	2
Operating Lease, Liability, Total	$ 2,300
Operating Lease, Right-of-Use Asset	$ 2,300
Houston, Texas [Member]
Area of Real Estate Property | ft²	38,300