Note 8 - Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2015

Notes Tables

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2014		1,235,526		$	4.19		7.1	$	7,709
Granted		526,591		$	12.29
Exercised		(4,158	)	$	1.83
Outstanding at June 30, 2015		1,757,959		$	6.62		7.5	$	19,772
Exercisable at June 30, 2015		751,204		$	3.14		5.2	$	11,066
Vested or expected to vest at June 30, 2015 (1)		1,650,391		$	6.48		7.4	$	18,802