Note 7 - Stockholders' Equity (Details Textual) - USD ($)		1 Months Ended	3 Months Ended		9 Months Ended
	May 30, 2018	Mar. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Number of Shares Authorized to Issue			185,000,000		185,000,000
Common Stock, Shares Authorized			175,000,000		175,000,000		175,000,000
Common Stock, Par or Stated Value Per Share			$ 0.18		$ 0.18		$ 0.18
Preferred Stock, Shares Authorized			10,000,000		10,000,000		10,000,000
Preferred Stock, Par or Stated Value Per Share			$ 0.001		$ 0.001		$ 0.001
Preferred Stock, Shares Issued, Total			671		671		2,379
Class of Warrant or Right, Outstanding			1,070,028		1,070,028
Class of Warrant or Right, Exercise Price of Warrants or Rights			$ 4.05		$ 4.05
Proceeds from Warrant Exercises		$ 11,300,000			$ 11,336,710
Class of Warrant or Right, Exercised During Period			0	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			5		1,708
Conversion of Stock, Shares Issued			1,421		485,244
Convertible Preferred Stock, Shares Issued upon Conversion			284		284
The 2018 Subscription Rights Offering [Member]
Number of Units Sold	13,624
Proceeds from Issuance of Stock units	$ 12,300,000
The 2018 Subscription Rights Offering [Member] | The 2018 Warrants [Member]
Class of Warrant or Right, Outstanding	3,869,216
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	$ 4.05
Series A Junior Participating Preferred Stock [Member]
Preferred Stock, Shares Authorized			750,000		750,000
Preferred Stock, Par or Stated Value Per Share			$ 0.001		$ 0.001
Preferred Stock, Shares Issued, Total			0		0
Series A Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized			4,000		4,000
Preferred Stock, Par or Stated Value Per Share			$ 0.001		$ 0.001
Series B Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized			25,000		25,000
Preferred Stock, Par or Stated Value Per Share			$ 0.001		$ 0.001
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