Note 9 - Stockholders' Equity and Stock-based Compensation Expense (Tables)

6 Months Ended

Jun. 30, 2018

Notes Tables

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

			Options Outstanding
	Shares Available for Grant		Number of Stock Options Outstanding		Weighted- Average Exercise Price
Balance, December 31, 2017		1,494,865		839,919	$	16.46
Options granted		(21,010)		21,010		50.65
Stock awards granted (1)		(395,511)		—		—
Options exercised		—		(188,859)		9.98
Options canceled		43,833		(43,833)		20.33
Stock awards canceled (1)		93,390		—		—
Balance, June 30, 2018		1,215,567		628,237	$	19.28

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

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2018		2017		2018		2017
Cost of revenue	$	227	$	147	$	380	$	276
Sales and marketing
Employee		660		401		1,112		821
Non-Employee		55		—		92		—
Research and development		262		239		453		476
General and administrative		1,002		444		1,856		1,053
Total stock-based compensation expense	$	2,206	$	1,231	$	3,893	$	2,626