Note 11 - Stock Based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Outstanding at January 1, 2015 (in shares)	2,139,822	1,744,755
Outstanding at January 1, 2015 (in dollars per share)	$ 5.64	$ 7.20
Granted (in shares)	846,283	839,250
Granted (in dollars per share)	$ 1.29	$ 2.35
Canceled or expired (in shares)	(53,442)	(444,183)
Canceled or expired (in dollars per share)	$ 9.71	$ 5.56
Outstanding at December 31, 2016 (in shares)	2,932,663	2,139,822
Outstanding at December 31, 2016 (in dollars per share)	$ 4.31	$ 5.64
Outstanding at December 31, 2016 (Year)	7 years 73 days
Exercisable at December 31, 2016 (in shares)	2,198,907
Exercisable at December 31, 2016 (in dollars per share)	$ 5.09
Exercisable at December 31, 2016 (Year)	6 years 328 days