Note 10 - Benefit Plans (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0	$ 0
Minimum [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	1.00%
Maximum [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	100.00%