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 ($)
9 Months Ended
Mar. 22, 2017
Jun. 17, 2016
Sep. 30, 2017
Sep. 30, 2016
May 22, 2017
Dec. 31, 2016
May 10, 2016
Dec. 31, 2015
Proceeds from Issuance of Common Stock     $ 31,440,000 $ 13,886,000        
Common Stock, Par or Stated Value Per Share     $ 0.0001     $ 0.0001 $ 0.0001  
Retained Earnings (Accumulated Deficit)     $ (95,357,000)     $ (68,622,000) [1]    
Cash and Cash Equivalents, at Carrying Value     19,207,000 $ 14,011,000   $ 8,086,000 [1]   $ 7,360,000
The 2017 Loan Agreement [Member] | CRG LP [Member]                
Debt Agreement, Covenant, Additional Funding     $ 10,000,000   $ 10,000,000      
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              
June 2016 Offering [Member]                
Stock Issued During Period, Shares, New Issues   3,105,000            
Share Price   $ 5            
Proceeds from Issuance of Common Stock   $ 15,525,000            
Proceeds From Issuance of Common Stock, Net   $ 13,886,000            
[1] The condensed consolidated balance sheet as of December 31, 2016 has been derived from the audited consolidated financial statements as of that date.