Note 3 - Summary of Status of Options and Warrants Outstanding (Details) - $ / shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2014
Stock Options One [Member]
Range of exercise prices, options (in dollars per share)	$ 0.17
Shares, options (in shares)	117,648
Weighted average remaining life, options	10 years
Stock Options Two [Member]
Range of exercise prices, options (in dollars per share)	$ 0.75
Shares, options (in shares)	7,333
Weighted average remaining life, options	5 years 98 days
Stock Options Three [Member]
Range of exercise prices, options (in dollars per share)	$ 2.63
Shares, options (in shares)	217,685
Weighted average remaining life, options	9 years 204 days
Stock Options Four [Member]
Range of exercise prices, options (in dollars per share)	$ 2.94
Shares, options (in shares)	30,614
Weighted average remaining life, options	9 years 277 days
Stock Options Five [Member]
Range of exercise prices, options (in dollars per share)	$ 3.10
Shares, options (in shares)	59,681
Weighted average remaining life, options	9 years 91 days
Stock Options Six [Member]
Range of exercise prices, options (in dollars per share)	$ 3.21
Shares, options (in shares)	6,232
Weighted average remaining life, options	9 years 186 days
Stock Options Seven [Member]
Range of exercise prices, options (in dollars per share)	$ 3.45
Shares, options (in shares)	7,245
Weighted average remaining life, options	9 years 3 days
Stock Options Eight [Member]
Range of exercise prices, options (in dollars per share)	$ 4.875
Shares, options (in shares)	134
Weighted average remaining life, options	6 years 346 days
Stock Options Nine [Member]
Range of exercise prices, options (in dollars per share)	$ 5.25
Shares, options (in shares)	2,031
Weighted average remaining life, options	6 years 160 days
Stock Options Ten [Member]
Range of exercise prices, options (in dollars per share)	$ 5.625
Shares, options (in shares)	192,000
Weighted average remaining life, options	6 years 350 days
Stock Options Eleven [Member]
Range of exercise prices, options (in dollars per share)	$ 5.925
Shares, options (in shares)	23,206
Weighted average remaining life, options	6 years 354 days
Stock Options Twelve [Member]
Range of exercise prices, options (in dollars per share)	$ 6
Shares, options (in shares)	123,998
Weighted average remaining life, options	6 years 138 days
Stock Options Thirteen [Member]
Range of exercise prices, options (in dollars per share)	$ 6.50
Shares, options (in shares)	3,845
Weighted average remaining life, options	8 years 277 days
Stock Options Fourteen [Member]
Range of exercise prices, options (in dollars per share)	$ 8.25
Shares, options (in shares)	3,636
Weighted average remaining life, options	8 years 186 days
Stock Options Fifteen [Member]
Range of exercise prices, options (in dollars per share)	$ 9.9375
Shares, options (in shares)	3,019
Weighted average remaining life, options	7 years 105 days
Stock Options Sixteen [Member]
Range of exercise prices, options (in dollars per share)	$ 10.50
Shares, options (in shares)	3,238
Weighted average remaining life, options	7 years 105 days
Stock Options Seventeen [Member]
Range of exercise prices, options (in dollars per share)	$ 11.25
Shares, options (in shares)	13,666
Weighted average remaining life, options	6 years 310 days
Stock Options Eighteen [Member]
Range of exercise prices, options (in dollars per share)	$ 12.75
Shares, options (in shares)	67
Weighted average remaining life, options	7 years 40 days
Stock Options Nineteen [Member]
Range of exercise prices, options (in dollars per share)	$ 13.875
Shares, options (in shares)	2,160
Weighted average remaining life, options	8 years 3 days
Stock Options Twenty [Member]
Range of exercise prices, options (in dollars per share)	$ 17.25
Shares, options (in shares)	40,261
Weighted average remaining life, options	7 years 343 days
Stock Options Twenty One [Member]
Range of exercise prices, options (in dollars per share)	$ 18.75
Shares, options (in shares)	3,334
Weighted average remaining life, options	7 years 328 days
Stock Options Twenty Two [Member]
Range of exercise prices, options (in dollars per share)	$ 20.25
Shares, options (in shares)	4,940
Weighted average remaining life, options	7 years 277 days
Stock Options Twenty Three [Member]
Range of exercise prices, options (in dollars per share)	$ 21.75
Shares, options (in shares)	1,336
Weighted average remaining life, options	7 years 189 days
Stock Options Twenty Four [Member]
Range of exercise prices, options (in dollars per share)	$ 23.85
Shares, options (in shares)	1,260
Weighted average remaining life, options	7 years 182 days
Warrant One [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 3.75
Class of Warrant or Right, Outstanding	56,381
Weighted average remaining life, warrants	1 year 346 days
Warrant Two [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 4.95
Class of Warrant or Right, Outstanding	2,830,627
Weighted average remaining life, warrants	4 years 153 days
Warrant Three [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 6
Class of Warrant or Right, Outstanding	102,857
Weighted average remaining life, warrants	1 year 346 days
Warrant Four [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 9
Class of Warrant or Right, Outstanding	2,666
Weighted average remaining life, warrants	1 year 299 days
Warrant Five [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 9.75
Class of Warrant or Right, Outstanding	63,232
Weighted average remaining life, warrants	3 years 127 days
Warrant Six [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 11.25
Class of Warrant or Right, Outstanding	147,420
Weighted average remaining life, warrants	1 year 255 days
Warrant Seven [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 12.375
Class of Warrant or Right, Outstanding	71,257
Weighted average remaining life, warrants	3 years 131 days
Warrant Eight [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 12.38
Class of Warrant or Right, Outstanding	5,557
Weighted average remaining life, warrants	3 years 222 days
Warrant Nine [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 13.50
Class of Warrant or Right, Outstanding	4,444
Weighted average remaining life, warrants	2 years 80 days
Warrant Ten [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 14.85
Class of Warrant or Right, Outstanding	23,612
Weighted average remaining life, warrants	2 years 58 days
Warrant Eleven [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 20.25
Class of Warrant or Right, Outstanding	1,481
Weighted average remaining life, warrants	2 years 321 days
Warrant Twelve [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 24.375
Class of Warrant or Right, Outstanding	21,538
Weighted average remaining life, warrants	2 years 310 days
Shares, options (in shares)	868,570
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 11.25
Class of Warrant or Right, Outstanding	3,331,072