Note 13 - 401(k) Savings Plan (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Employee Eligible Service Period	30 days
Defined Benefit Plan, Eligible Age for Employee	21 years
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	50.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	6.00%
Defined Contribution Plan, Employee Eligible Service Period for Employer Match	180 days
Defined Contribution Plan, Cost	$ 173,000	$ 169,000	$ 143,000