Note 15 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive securities (in shares)	4,311,096	3,491,937	19,283,456
Convertible Preferred Stock [Member]
Antidilutive securities (in shares)			9,208,376
Convertible Debt Securities [Member]
Antidilutive securities (in shares)			8,731,657
Warrant [Member]
Antidilutive securities (in shares)			194,383
Employee Stock Option [Member]
Antidilutive securities (in shares)	4,213,100	3,491,937	1,149,040
Restricted Stock Units (RSUs) [Member]
Antidilutive securities (in shares)	97,996