Note 13 - Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2016
Notes Tables  
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]
 
 
Number of Unvested Restricted Shares of Common Stock and Restricted Stock
Units
 
 
Weighted Average
Grant Date Fair
Value
 
                 
Unvested shares as of January 1, 2016
    
430,816
    $
13.08
 
Granted
    
200,622
    $
26.31
 
Vested
    
(109,503
 )   $
8.12
 
Forfeited
    
(19,162
 )   $
15.49
 
Unvested shares as of December 31, 2016
    
502,773
    $
19.35