Note 9 - Acquired Intangible Assets, Net (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amortization of Intangible Assets, Total	$ 1.0	$ 1.0	$ 1.1
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	1.0
Finite-Lived Intangible Assets, Amortization Expense, Year Two	1.0
Finite-Lived Intangible Assets, Amortization Expense, Year Five	2.1
Finite-Lived Intangible Assets, Amortization Expense, Year Three	1.0
Finite-Lived Intangible Assets, Amortization Expense, Year Four	$ 1.0