Note 15 - Income Taxes (Details Textual) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%
Operating Income (Loss)			$ (7,311,000)	$ (10,982,000)	$ (21,137,000)
Deferred Tax Assets, Gross			28,580,000	38,677,000
Deferred Tax Assets, Valuation Allowance			$ 28,545,000	$ 38,645,000
Accounting Standards Update 2016-09 [Member]
Operating Income (Loss)	$ (1,100,000)
Deferred Tax Assets, Gross	400,000
Deferred Tax Assets, Valuation Allowance	$ 400,000
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%