Note 4 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Percentage Of Income Tax Examination Likelihood Of Tax Benefits Being Realized Upon Settlement	50.00%
Unrecognized Tax Benefits, Ending Balance	$ 0	$ 0	$ 0
Preferred Stock, Dividend Rate, Percentage	10.00%
Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member]
Property, Plant and Equipment, Useful Life	7 years