Note 7 - Employee Benefit and Savings Plan (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0	$ 0	$ 0
100% Matching [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	100.00%	100.00%	100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	3.00%	3.00%	3.00%
50% Matching [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%	50.00%	50.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	2.00%	2.00%	2.00%