Annual report pursuant to Section 13 and 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 ($)
1 Months Ended 2 Months Ended 12 Months Ended 14 Months Ended
Feb. 12, 2018
Nov. 08, 2017
Mar. 22, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2018
Jun. 08, 2018
Jan. 01, 2018
Dec. 31, 2016
Shares Issued, Price Per Share                 $ 2.56    
Proceeds from Issuance of Common Stock           $ 53,792,000 $ 31,565,000        
Cash and Cash Equivalents, at Carrying Value, Ending Balance       $ 29,523,000 $ 20,730,000 29,523,000 20,730,000 $ 29,523,000     $ 8,086,000
Working Capital       31,144,000   31,144,000   31,144,000      
Net Cash Provided by (Used in) Operating Activities, Total           (43,090,000) (34,853,000)        
Retained Earnings (Accumulated Deficit), Ending Balance       $ (155,385,000) $ (105,581,000) $ (155,385,000) $ (105,581,000) $ (155,385,000)   $ (105,404,000)  
December 2018 Offering [Member]                      
Stock Issued During Period, Shares, New Issues       14,728,504              
Shares Issued, Price Per Share       $ 1.50   $ 1.50   $ 1.50      
Proceeds from Issuance of Common Stock       $ 22,093,000              
Proceeds From Issuance of Common Stock, Net       $ 20,385,000              
February 2018 Offering [Member]                      
Stock Issued During Period, Shares, New Issues 11,500,000                    
Shares Issued, Price Per Share $ 3                    
Proceeds from Issuance of Common Stock $ 34,500,000                    
Proceeds From Issuance of Common Stock, Net $ 32,214,000                    
November 2017 ATM Facility [Member]                      
Stock Issued During Period, Shares, New Issues         59,249 277,249 59,249 336,498      
Proceeds From Issuance of Common Stock, Net           $ 1,193,000 $ 125,000 $ 1,318,000      
Aggregate Offering Price   $ 25,000,000                  
March 2017 Offering [Member]                      
Stock Issued During Period, Shares, New Issues     8,625,000                
Shares Issued, Price Per Share     $ 4                
Proceeds from Issuance of Common Stock     $ 34,500,000                
Proceeds From Issuance of Common Stock, Net     $ 31,440,000