Note 6 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2016

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, 2015		2,200,369		$	8.52		7.8	$	15,705
Granted		119,162		$	6.90
Exercised		(80,825	)	$	1.91
Cancelled or forfeited		(69,089	)	$	14.12
Outstanding at September 30, 2016		2,169,617		$	8.50		7.3	$	5,814
Exercisable at September 30, 2016		1,055,385		$	5.81		5.8	$	4,619
Vested or expected to vest at September 30, 2016 (1)		2,033,481		$	8.29		7.2	$	5,697

Common Stock Reserved for Future Issuance [Table Text Block]

	September 30, 2016		December 31, 2015
Stock-based compensation awards		2,999,166		2,419,901
Employee Stock Purchase Plan		296,685		297,359
Total		3,295,851		2,717,260