Note 6 - Goodwill and Acquired Intangible Assets - Acquired Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Net Carrying Amount, Finite-Lived Intangible Assets	$ 56	$ 61
Other Intangible Assets [Member]
Gross Carrying Amount, Finite-Lived Intangible Assets	668	652
Accumulated Amortization, Finite-Lived Intangible Assets	612	591
Net Carrying Amount, Finite-Lived Intangible Assets	$ 56	$ 61
Other Intangible Assets [Member] | Minimum [Member]
Amortization Period, Finite-Lived Intangible Assets (Year)	5 years	5 years
Other Intangible Assets [Member] | Maximum [Member]
Amortization Period, Finite-Lived Intangible Assets (Year)	10 years	10 years
Technology-Based Intangible Assets [Member]
Gross Carrying Amount, Finite-Lived Intangible Assets	$ 668	$ 652
Accumulated Amortization, Finite-Lived Intangible Assets	612	591
Net Carrying Amount, Finite-Lived Intangible Assets	$ 56	$ 61