Note 6 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			34.00%
Income Tax Expense (Benefit), Total	$ 0
Valuation Allowance Percentage	100.00%
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	$ 36,100		$ 34,500
Operating Loss Carryforwards, Valuation Allowance, Total	7,700		7,400
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	12,400		12,200
Operating Loss Carryforwards, Valuation Allowance, Total	$ 1,000		$ 200
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%