Note 6 - Common Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2016	Dec. 31, 2015
Performance Shares [Member]
Reserved for future issuance (in shares)	3,073,567	2,419,901
The 2014 Employee Stock Purchase Plan [Member]
Reserved for future issuance (in shares)	297,359	297,359
Reserved for future issuance (in shares)	3,370,926	2,717,260