Note 5 - Share-based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Notes Tables

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

Expected volatility	50.1%	-	53.2%
Expected dividends	None
Exercise price	$30.83	-	$42.65
Expected term (in years)	5.7	-	6.0
Risk-free rate	2.03%	-	2.24%

Expected volatility, including peer group	30.8%	-	81.6%
Expected dividends	None
30 calendar day volume weighted average stock price, including peer group	$2.13	-	$133.20
Expected term (in years)	3.0
Risk-free rate	1.94%	-	1.95%