Note 15 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allocated Share-based Compensation Expense	$ 1,443,346	$ 1,187,036	$ 947,174
Employee Stock Option
Allocated Share-based Compensation Expense	471,849	554,435	424,904
Restricted Stock
Allocated Share-based Compensation Expense	856,731	552,907	460,853
Employee Stock Purchase Plan
Allocated Share-based Compensation Expense	$ 114,766	$ 79,694	$ 61,417

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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