Note 9 - Convertible Preferred Stock, Stockholders' Equity and Common Stock Warrants (Details Textual) - USD ($)		1 Months Ended		12 Months Ended
	Jan. 22, 2018	Jan. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 13, 2017
Stock Issued During Period, Shares, Issued for Services				7,792	1,174
Stock Issued During Period, Shares, Conversion of Convertible Securities		553,752
Common Stock Dividends, Shares		68,815
Stock Issued During Period, Shares, Make-whole Adjustment		777,895
Dividends, Make-whole Adjustment		$ 8,200,000		$ 8,167,895
Proceeds from Issuance of Convertible Preferred Stock, Net of Offering Costs					22,129,774
Warrant Expense					$ 10,225,846
Stock Repurchased and Retired During Period, Shares				0	0
Class of Warrant or Rights, Expired				28,123	867
Series A Preferred Stock [Member]
Proceeds from Issuance of Private Placement					$ 0
Preferred Stock, Shares Authorized				0		13,750,000
Preferred Stock, Shares Issued, Total				0
Preferred Stock, Shares Outstanding, Ending Balance				0
Conversion From Series A Preferred Stock to Common Stock [Member]
Conversion of Stock, Shares Issued	1,400,462	1,400,462
Warrants Issued in Connection with the January 2018 Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	1,000,000	1,000,000
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 12	$ 12
Class of Warrant or Right, Term	5 years
Warrants Issued in Connection with the January 2018 Offering [Member] | Maximum [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 15
Option Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		150,000
Additional Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 12
Class of Warrant or Right, Granted		131,375
Underwriter Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 15	$ 15
Class of Warrant or Right, Term	5 years	5 years
Underwriter Warrants [Member] | Maximum [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	50,000	50,000
January 2018 Offering [Member]
Stock Issued During Period, Shares, New Issues	1,000,000	1,000,000
Proceeds from Issuance or Sale of Equity, Total	$ 10,800,000	$ 10,800,000
Stock Issued During Period, Shares, Issued for Services		150,000
January 2018 Offering [Member] | Additional Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	131,375
Private Placement [Member] | Warrant [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights			$ 33.30
Class of Warrant or Right, Term			5 years
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right			1
Warrant Expense					$ 10,200,000
Private Placement [Member] | Series A Preferred Stock [Member]
Proceeds from Issuance of Private Placement			$ 25,000,000
Number of Convertible Preferred Stock Per Unit			1
Preferred Stock, Dividend Rate, Percentage			8.00%
Number of Common Stock Per Unit			1
Convertible Preferred Stock, Conversion Price			$ 30.30
Temporary Equity, Stock Issued During Period, New Issues			12,376,329
Proceeds from Issuance of Convertible Preferred Stock, Net of Offering Costs			$ 22,100,000
Payments of Stock Issuance Costs			$ 2,900,000
Private Placement [Member] | Series B Preferred Stock [Member] | Placement Agent [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights			$ 33.30
Class of Warrant or Right, Term			5 years
Class of Warrant or Right, Granted During Period			78,637