Quarterly report pursuant to Section 13 or 15(d)

Note 1 - The Company and Basis of Presentation (Details Textual)

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Note 1 - The Company and Basis of Presentation (Details Textual) - USD ($)
3 Months Ended 6 Months Ended
Feb. 12, 2018
Nov. 08, 2017
Mar. 22, 2017
Jun. 30, 2018
Jun. 30, 2018
Jun. 30, 2017
Proceeds from Issuance of Common Stock         $ 33,396,000 $ 31,440,000
February 2018 Offering [Member]            
Stock Issued During Period, Shares, New Issues 11,500,000          
Share Price $ 3          
Proceeds from Issuance of Common Stock $ 34,500,000          
Proceeds From Issuance of Common Stock, Net $ 32,213,000          
November 2017 ATM Facility [Member]            
Stock Issued During Period, Shares, New Issues         332,778  
Proceeds From Issuance of Common Stock, Net         $ 1,308,000  
Aggregate Offering Price   $ 25,000,000        
ATM Facility [Member]            
Stock Issued During Period, Shares, New Issues       65,252 273,529  
Proceeds From Issuance of Common Stock, Net       $ 172,000 $ 1,183,000  
March 2017 Offering [Member]            
Stock Issued During Period, Shares, New Issues     8,625,000      
Share Price     $ 4      
Proceeds from Issuance of Common Stock     $ 34,500,000      
Proceeds From Issuance of Common Stock, Net     $ 31,440,000