Note 5 - Common Stock (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Mar. 31, 2017	Feb. 28, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock, No Par Value			$ 0	$ 0
Stock Issued During Period, Shares, New Issues	2,400,000	87,000
Shares Issued, Price Per Share	$ 13
Proceeds from Issuance of Common Stock	$ 31,600	$ 1,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period			160,500	406,667	204,159
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price			$ 2.50
Proceeds from Stock Options Exercised			$ 401	$ 703
Stockholders' Equity Note, Subscriptions Receivable			$ 200
Minimum [Member]
Shares Issued, Price Per Share		$ 12.09
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price				$ 2.50	$ 0.74
Maximum [Member]
Shares Issued, Price Per Share		$ 12.37
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price				$ 14.71	$ 19.09