Note 11 - Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Notes Tables

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

	Three Months Ended
	March 31,
	2018			2017
Expected terms (years)	6.0	-	6.5	5.95	-	9.93
Volatility	32.1	-	33.7%	33.8	-	40.6%
Risk-free rate	2.6	-	2.7%	2.1	-	2.4%
Dividend yield		—%			—%

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

							Weighted		Weighted
							Average		Average
	Options			Number of			Exercise		Remaining
	Available			Options			Price		Contractual
	for Grant			Outstanding			per Share		Life in Years
Balance — December 31, 2017		1,601,202			6,521,146		$	1.19		6.9
Additional shares reserved		1,918,868			—
Options granted		(1,802,704	)		1,802,704		$	1.32
Options forfeited/cancelled/repurchase		171,057			(171,057	)	$	2.35
Balance — March 31, 2018		1,888,423			8,152,793		$	1.20		7.3
Vested or expected to vest at March 31, 2018					7,734,708		$	1.17		7.2
Exercisable at March 31, 2018					4,490,966		$	0.81		5.6

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

	Three Months Ended
	March 31,
	2018		2017
Cost of goods sold	$	27	$	19
Research and development		26		11
Selling, general and administrative		157		93
Total	$	210	$	123