Note 8 - Options Outstanding Separated into Range of Exercise Price (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Range One [Member]
Lower range (in dollars per share)	$ 0.901	$ 0.07
Upper range (in dollars per share)	$ 1.576	$ 0.901
Outstanding (in shares)	978,178	594,591
Weighted average remaining contractual life, outstanding	2 years 336 days	2 years 183 days
Weighted average exercise price, outstanding (in dollars per share)	$ 1.224	$ 0.728
Exercisable (in shares)	978,178	594,591
Weighted average remaining contractual life, exercisable	2 years 336 days	2 years 183 days
Weighted average exercise price, exercisable (in dollars per share)	$ 1.224	$ 0.728
Range Two [Member]
Lower range (in dollars per share)	6.23	1.039
Upper range (in dollars per share)	$ 8.80	$ 1.576
Outstanding (in shares)	145,693	1,651,595
Weighted average remaining contractual life, outstanding	5 years 335 days	4 years 93 days
Weighted average exercise price, outstanding (in dollars per share)	$ 6.786	$ 1.261
Exercisable (in shares)	137,391	1,651,595
Weighted average remaining contractual life, exercisable	5 years 326 days	4 years 93 days
Weighted average exercise price, exercisable (in dollars per share)	$ 6.785	$ 1.261
Range Three [Member]
Lower range (in dollars per share)		6.23
Upper range (in dollars per share)		$ 8.80
Outstanding (in shares)	378,149	174,222
Weighted average remaining contractual life, outstanding	7 years 64 days	6 years 323 days
Weighted average exercise price, outstanding (in dollars per share)	$ 12.47	$ 6.724
Exercisable (in shares)	261,065	135,318
Weighted average remaining contractual life, exercisable	7 years 58 days	6 years 297 days
Weighted average exercise price, exercisable (in dollars per share)	$ 12.47	$ 6.739
Range Four [Member]
Lower range (in dollars per share)	19.51
Upper range (in dollars per share)	$ 21.66
Outstanding (in shares)	640,743	413,680
Weighted average remaining contractual life, outstanding	8 years 222 days	8 years 63 days
Weighted average exercise price, outstanding (in dollars per share)	$ 21.219	$ 12.47
Exercisable (in shares)	211,571	184,504
Weighted average remaining contractual life, exercisable	8 years 174 days	8 years 55 days
Weighted average exercise price, exercisable (in dollars per share)	$ 21.237	$ 12.47
Range Five [Member]
Lower range (in dollars per share)	22.01	21
Upper range (in dollars per share)	$ 24.23	$ 24.23
Outstanding (in shares)	309,222	1,039,073
Weighted average remaining contractual life, outstanding	8 years 108 days	9 years 173 days
Weighted average exercise price, outstanding (in dollars per share)	$ 22.293	$ 21.611
Exercisable (in shares)	127,326	54,446
Weighted average remaining contractual life, exercisable	8 years 102 days	8 years 296 days
Weighted average exercise price, exercisable (in dollars per share)	$ 22.365	$ 21.764
Range Six [Member]
Outstanding (in shares)	154,200	207,450
Weighted average remaining contractual life, outstanding	9 years 54 days	9 years 82 days
Weighted average exercise price, outstanding (in dollars per share)	$ 29.88	$ 39.86
Weighted average remaining contractual life, exercisable	0 years	0 years
Weighted average exercise price, exercisable (in dollars per share)	$ 0	$ 0
Range Seven [Member]
Outstanding (in shares)	176,375
Weighted average remaining contractual life, outstanding	8 years 82 days
Weighted average exercise price, outstanding (in dollars per share)	$ 39.86
Exercisable (in shares)	78,718
Weighted average remaining contractual life, exercisable	8 years 82 days
Weighted average exercise price, exercisable (in dollars per share)	$ 39.86
Outstanding (in shares)	2,782,560	4,080,611
Weighted average remaining contractual life, outstanding	6 years 89 days	6 years 33 days
Weighted average exercise price, outstanding (in dollars per share)	$ 14.026	$ 9.697
Exercisable (in shares)	1,794,249	2,620,454
Weighted average remaining contractual life, exercisable	5 years 12 days	4 years 131 days
Weighted average exercise price, exercisable (in dollars per share)	$ 8.841	$ 2.638