Note 11 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	1 Months Ended	3 Months Ended
	Oct. 31, 2018	Mar. 31, 2017	Mar. 31, 2019	Dec. 31, 2018
Common Stock, Shares Authorized			160,000	160,000
Common Stock, Par or Stated Value Per Share			$ 0.0013	$ 0.0013
Preferred Stock, Shares Authorized			20,000	20,000
Preferred Stock, Par or Stated Value Per Share			$ 0.001	$ 0.001
Replacement Shelf Registration	$ 250	$ 250
Common Stock Sales Agreement with Agent, Maximum Aggregate Offering Price	$ 75	$ 75