Note 8 - Common Stock - Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reserved for future issuance (in shares)	3,275,291	2,717,260
The 2014 Employee Stock Purchase Plan [Member]
Reserved for future issuance (in shares)	292,821	297,359	140,500
Performance Shares [Member]
Reserved for future issuance (in shares)	2,982,470	2,419,901