Note 5 - Share-based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Notes Tables

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

	Three Month Period Ended
	March 31, 2018
				Wtd. Avg.
				Exercise
	Options			Price
Outstanding at beginning of year		2,390,012		$	1.85
Granted		—		$	N/A
Exercised		(62,438	)	$	1.16
Forfeited		(730	)	$	2.62
Expired		—		$	N/A
Outstanding at March 31, 2018		2,326,844		$	1.87
Stock options exercisable at March 31, 2018		1,637,951		$	1.76

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Three Month Period Ended
	March 31,
	201 8		201 7
Risk free interest rate		N/A		2.07	%
Dividend yield		N/A		0.0	%
Expected term (in years)		N/A		5.18
Volatility		N/A		75	%

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

	Three Month Period Ended
	March 31, 2018
	Number of Restricted Shares			Grant-Date Fair Value
Unvested outstanding at beginning of year		237,926		$	1.79
Granted		161,768		$	6.00
Vested		(55,613	)	$	1.78
Forfeited		(6,100	)	$	1.76
Unvested outstanding at March 31, 2018		337,981		$	3.80

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	Three Month Period Ended
	March 31,
	2018		2017
Research and development costs	$	65,595	$	59,265
Sales and marketing costs		68,513		59,619
General and administrative costs		190,949		168,198
Cost of product sales		48,368		42,813
Total	$	373,425	$	329,895