Note 6 - Series A Preferred Financing (Details Textual) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended
	Aug. 02, 2017	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Preferred Stock, Par or Stated Value Per Share		$ 0.001		$ 0.001	$ 0.001
Common Stock [Member]
Stock Issued During Period, Shares, Conversion of Convertible Securities			341,743	341,743
Series A Convertible Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues	22,000
Preferred Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001		$ 0.001
Shares Issued, Price Per Share	$ 1,000
Proceeds from Issuance of Convertible Preferred Stock	$ 22.0
Payments of Stock Issuance Costs	$ 0.5
Convertible Preferred Stock, Shares Issued upon Conversion	1,005
Convertible Preferred Stock, Conversion Price of Shares Issued upon Conversion	$ 0.9949
Convertible Preferred Stock, Maximum Ownership Percentage Allowed after Conversion of Stock	9.985%
Preferred Stock, Redemption Price Per Share	$ 1.30
Accretion of Redeemable Convertible Preferred Stock to Redemption Value	$ 6.7
Conversion of Stock, Shares Converted				340
Preferred Stock, Shares Issued, Total		21,660		21,660	22,000
Preferred Stock, Shares Outstanding, Ending Balance		21,660		21,660	22,000