Note 7 - Stock-based Compensation (Details) - Stock Option Activity for Employees and Non-employees (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Stock Option Activity for Employees and Non-employees [Abstract]
Options	1,635,219		1,235,526
Weighted-Average Exercise Price	$ 5.76		$ 4.19
Weighted-Average Remaining Contractual Term (years)	7 years 219 days		7 years 36 days
Aggregate Intrinsic Value	$ 9,632		$ 7,709
Granted	399,929
Granted	$ 10.61
Exercised	(236)
Exercised	$ 1.27
Exercisable at March 31, 2015	593,324
Exercisable at March 31, 2015	$ 2.38
Exercisable at March 31, 2015	4 years 146 days
Exercisable at March 31, 2015	5,505
Vested or expected to vest at March 31, 2015 (1)	1,526,587	[1]
Vested or expected to vest at March 31, 2015 (1)	$ 5.65	[1]
Vested or expected to vest at March 31, 2015 (1)	7 years 146 days	[1]
Vested or expected to vest at March 31, 2015 (1)	$ 9,153	[1]

[1] Represents the number of vested options at March 31, 2015 plus the number of unvested options expected to vest based on the unvested options outstanding at March 31, 2015.