Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) (USD $)
 1 Months Ended 12 Months Ended 1 Months Ended
Feb. 28, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jul. 31, 2013
Apr. 30, 2012
Aug. 31, 2012
Nov. 30, 2013
Oct. 31, 2013
Aug. 31, 2013
Sep. 02, 2014
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Common Stock, Shares Authorized   200,000,000 120,000,000                
Temporary Equity, Shares Authorized   0 160,700,000                
Preferred Stock, Shares Authorized   5,000,000 0                
Stock Issued During Period, Shares, New Issues 6,228,725                    
Share Price (in Dollars per share) $ 8.00 $ 10.00                 $ 9.83
Proceeds from Issuance Initial Public Offering (in Dollars) $ 49,800,000 $ 49,829,800                  
Payments of Stock Issuance Costs (in Dollars)   4,875,404 1,501,344 208,934              
Temporary Equity, Shares Outstanding   0                  
Preferred Stock, Shares Issued   0 0                
Stock Issued During Period, Value, New Issues (in Dollars)   49,829,800                  
Debt Conversion, Original Debt, Amount (in Dollars)       10,668,185              
Class of Warrant or Right, Number of Securities Called by Warrants or Rights   9,598 9,598                
Class of Warrant or Right, Exercise Price of Warrants or Rights (in Dollars per share)   $ 6.60 $ 6.60                
Underwriting Discounts and Commissions [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Payments of Stock Issuance Costs (in Dollars) 3,500,000                    
Other Offering Expenses [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Payments of Stock Issuance Costs (in Dollars) 2,900,000                    
Series D Redeemable Convertible Preferred Stock [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Stock Issued During Period, Shares, New Issues     6,373,782 2,549,897 6,373,782            
Temporary Equity, Shares Outstanding     21,040,817 8,137,739              
Stock Issued During Period, Value, New Issues (in Dollars)     11,446,143 4,793,806   19,700,000          
Debt Conversion, Original Debt, Amount (in Dollars)           10,700,000          
Conversion of Stock, Shares Converted   21,040,817                  
Preferred Stock, Liquidation Preference Per Share (in Dollars per share)         $ 1.978565            
Series D-1 Redeemable Convertible Preferred Stock [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Stock Issued During Period, Shares, New Issues       3,713,333     3,716,935        
Share Price (in Dollars per share)             $ 4.298725        
Temporary Equity, Shares Outstanding       7,433,870              
Stock Issued During Period, Value, New Issues (in Dollars)       7,842,733     16,000,000        
Series E Redeemable Convertible Preferred Stock [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Stock Issued During Period, Shares, New Issues     36,856,922         19,037,063 921,423 16,898,436  
Temporary Equity, Shares Outstanding     56,011,258                
Stock Issued During Period, Value, New Issues (in Dollars)     47,409,867         24,792,595 1,200,000 22,007,404  
Conversion of Stock, Shares Converted   56,011,258                  
Preferred Stock [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Preferred Stock, Shares Issued   0                  
Conversion of Redeemable Convertible Preferred Stock to Common Stock [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Conversion of Stock, Shares Issued 13,188,251                    
Conversion of Series D-1 Preferred Stock to Series D Preferred Stock [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Conversion of Stock, Shares Issued         16,151,212            
Conversion of Stock, Shares Converted         7,433,870            
Net of Discounts and Commissions [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Proceeds from Issuance Initial Public Offering (in Dollars) $ 43,400,000                    
Additional Shares [Member]                      
Note 10 - Common Stock, Redeemable Convertible Preferred Stock and Preferred Stock (Details) [Line Items]                      
Stock Issued During Period, Shares, New Issues 603,725