Note 12 - Stockholders' Equity - Changes in Stockholders' Equity (Details) - Common Stock [Member]
12 Months Ended
Dec. 31, 2016
shares
Exercise of stock options and restricted stock awards (in shares) 437,930
Conversion of preferred stock to common stock (in shares) 2,014,538
Total shares of common stock reserved for future issuance (in shares) 2,501,676
Performance Restricted Stock Units [Member]  
Issuance of Performance Restricted Stock Units (in shares) 49,208