Note 7 - Net Loss Per Common Share - Earnings Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Basic and diluted weighted average common stock shares outstanding (in shares)	14,098,610	12,964,639
Employee Stock Option [Member]
Potentially dilutive securities excluded from loss per share computations (in shares)	3,326,841	3,387,581
Warrant [Member]
Potentially dilutive securities excluded from loss per share computations (in shares)	6,676,849	7,603,141
Restricted Stock [Member]
Potentially dilutive securities excluded from loss per share computations (in shares)	337,981	282,350