Note 9 - Stockholders' Equity (Details Textual)		1 Months Ended	3 Months Ended	12 Months Ended
	May 30, 2018 USD ($) $ / shares shares	Mar. 31, 2019 USD ($)	Mar. 31, 2019 shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	May 29, 2018 $ / shares shares	May 09, 2018 USD ($) shares	May 19, 2014 $ / shares shares
Number of Shares Authorized to Issue				185,000,000
Common Stock, Shares Authorized				175,000,000	175,000,000
Common Stock, Par or Stated Value Per Share | $ / shares				$ 0.18	$ 0.18
Preferred Stock, Shares Authorized				10,000,000	10,000,000
Preferred Stock, Par or Stated Value Per Share | $ / shares				$ 0.001	$ 0.001
Preferred Stock, Shares Issued, Total				671	2,379
Stockholder Rights Agreement, Number of Preferred Stock Right Distributed for Each Share of Common Stock								1
Stockholder Rights Agreement, Acquiring Person, Percentage of Ownership								15.00%
Stockholder Rights Agreement, Acquiring Person, Additional Percentage of Ownership								2.00%
Stockholder Rights Agreement, Initial Exercise Price of Each Right | $ / shares								$ 15
Stockholder Rights Agreement, Share Price | $ / shares								$ 30
Class of Warrant or Right, Outstanding				1,070,028
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares				$ 4.05
Consummate a Business Combination, Percentage of Acquired Outstanding Shares				50.00%
Consummate a Business Combination, Percentage of Aggregate Ordinary Voting Power				50.00%
Preferred Stock, Deemed Dividend | $					$ 11,479,308
Proceeds from Warrant Exercises | $		$ 11,300,000		$ 11,336,710
Class of Warrant or Right, Exercised During Period			2,800,000
Stock Issued During Period, Shares, Warrant Exercised			2,800,000
Conversion of Series B Convertible Preferred Stock into Common Stock [Member]
Conversion of Stock, Shares Converted				1,708	11,245
Conversion of Stock, Shares Issued				485,244	3,194,600
Convertible Preferred Stock, Shares Issued upon Conversion				284
The 2018 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right				1
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares				$ 4.05
Warrants and Rights Outstanding, Term				4 years
Warrants Exercisable, Ownership Percentage of Company’s Shares Allowed				4.99%
Common Stock, Convertible, Ownership Percentage of Company’s Shares Allowed				9.99%
Warrants and Rights Outstanding, Redemption Price | $ / shares				$ 0.18
Warrants and Rights Outstanding, Redeemable, Volume-weighted-average-price of Our Common Stock | $ / shares				$ 10.56
Warrants and Rights, Redemption Rights, Consecutive Trading Days				10
The 2018 Subscription Rights Offering [Member]
Number of Units Authorized to Purchase, Maximum							25,000
Purchase Price of Unit | $							$ 1,000
Number of Series B Convertible Preferred Stock and Warrant in Each Unit							1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right							284
Number of Units Sold	13,624
Proceeds from Issuance of Stock units | $	$ 12,300,000
Adjustments to Additional Paid in Capital, Beneficial Conversion Feature on Preferred Stock | $					$ 4,782,100
Preferred Stock, Deemed Dividend | $					11,479,308
Payments of Stock Issuance Costs | $					1,333,449
The 2018 Subscription Rights Offering [Member] | The 2018 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right	1
Class of Warrant or Right, Outstanding	3,869,216
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	$ 4.048
Warrants Allocated to Common Stock , Net of Issuance Cost | $					$ 5,363,759
Series B Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized						25,000
Preferred Stock, Par or Stated Value Per Share | $ / shares						$ 0.001
Series A Junior Participating Preferred Stock [Member]
Preferred Stock, Shares Authorized				750,000
Preferred Stock, Par or Stated Value Per Share | $ / shares				$ 0.001
Preferred Stock, Shares Issued, Total				0	0
Series A Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized				4,000
Preferred Stock, Par or Stated Value Per Share | $ / shares				$ 0.001
Series B Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized				25,000
Preferred Stock, Par or Stated Value Per Share | $ / shares				$ 0.001
Stated Value per Share | $				$ 1,000
Preferred Stock, Convertible, Conversion Price | $ / shares				$ 3.52
Preferred Stock, Convertible, Ownership Percentage of Company’s Shares Allowed				9.99%
Series B Convertible Preferred Stock [Member] | The 2018 Subscription Rights Offering [Member]
Stock Issued During Period, Shares, New Issues	13,624
Sale of Series A Convertible Preferred Stock [Member]
Preferred Stock, Shares Issued, Total				0	0